Thymidylate synthase expression is closely associated with outcome in patients with pulmonary adenocarcinoma.

The aim of this study is to elucidate the prognostic significance of thymidylate synthase (TS), orotate phosphoribosyltransferase (OPRT) and dihydropyrimidine dehydrogenase (DPD) in completely resected non-small cell lung cancer (NSCLC). One hundred and sixty patients with NSCLC were included in this study. Tumor sections were stained by immunohistochemistry for TS, OPRT, DPD, glucose transporter 1 (Glut1), hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), microvessel density (MVD) determinated by CD34, epidermal growth factor receptor (EGFR), phosph-Akt, phosph-mammalian target of rapamycin (mTOR) and p53. TS, OPRT and DPD were positively expressed in 46, 71 and 54%, respectively. The expression of TS and OPRT was significantly higher in patients with non-adenocarcinoma (non-AC) (n = 53) than adenocarcinoma (AC) (n = 107), and DPD expression was higher in adenocarcinoma as compared with non-adenocarcinoma. A positive TS expression was an independent prognostic factor for predicting a poor outcome in patients with AC, but not in those with non-AC. In AC patients, TS expression was significantly associated with advanced stage, lymph node metastases, vascular invasion, Glut1, HIF-1α, angiogenesis, EGFR signaling pathway and p53. In patients with non-AC, TS expression was not closely correlated with outcome and these biomarkers. A positive TS expression was a powerful prognostic factor to predict a poor outcome in completely resected AC patients.

Biomarker analysis in patients with advanced gastric cancer treated with S-1 plus cisplatin chemotherapy: orotate phosphoribosyltransferase expression is associated with treatment outcomes.

This study was performed to analyze the impact of protein expression related to fluoropyrimidine and cisplatin metabolism (thymidylate synthase, dihydropyrimidine dehydrogenase, thymidine phosphorylase, orotate phosphoribosyltransferase [OPRT], excision repair cross-complementation 1, Fanconi anemia complementation group D2, glutathione S-transferase P1, and X-ray repair cross-complementing group 1) on treatment outcomes in patients with metastatic or relapsed gastric cancer (MRGC) receiving S-1/cisplatin chemotherapy. Protein expression was measured by immunohistochemistry (IHC). Of the 43 patients who had received S-1 (80 mg/m2/day; days 1-14) and cisplatin (60 mg/m2; day 1) every 3 weeks and had available tissue blocks, IHC was successfully performed in 41 patients. Patients with high OPRT levels in tumor tissues (IHC score≥6) had superior progression-free survival (PFS) (23.3 vs. 14.1 weeks [median]) and overall survival (OS) (72.4 vs. 55.4 weeks [median]) to those with low OPRT levels (IHC score≤5; P-values<.05). Expression levels of other proteins were not predictive of treatment outcomes. In multivariate analysis, both a good performance status and a high OPRT level were independently associated with prolonged PFS and OS. The OPRT expression level may be a good predictive marker in S-1/cisplatin-treated patients with MRGC.

The effect of neoadjuvant therapy on the 5-fluorouracil metabolic and relative enzymes of oral squamous cell carcinoma.

To assess the effect of neoadjuvant therapy using tegafur/uracil (UFT) and radiation therapy on the 5-fluorouracil (5-FU) metabolic and relative enzymes, thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), orotate phosphoribosyl transferase (OPRT) and thymidine phosphorylase (TP) in oral squamous cell carcinoma (OSCC), we examined the mRNA expression and immunohistochemical staining status of these enzymes using 17 surgical specimens. Seven patients did not receive any neoadjuvant therapy and 10 were treated with UFT and local irradiation therapy. Our result showed that the mRNA expression of these enzymes in neoadjuvant group was not significantly different from that of non-treated group using real-time quantitative PCR. To confirm the protein expression, we also carried out immunohistological staining of TS and DPD two key enzymes in the 5-FU metabolism, using the same specimens. Immunohistological staining status did not correspond to the results of mRNA analysis completely, though no significant difference between the groups was observed. Furthermore, no significant relationship between the UFT administration period and mRNA expression of the 5-FU metabolic enzymes was observed in neoadjuvant therapy group and also the distribution of the enzyme mRNA expression levels was similar to that of non-treated group. The results suggested that the neoadjuvant therapy of OSCC might not affect the expression status of 5-FU metabolic and relative enzymes in surgical tumor samples and the tumor tissues might serve as a useful specimen source to analyze the expression status of the 5-FU metabolic and relative enzymes and to determine the prospective efficiency of 5-FU-based adjuvant chemotherapy.

Predictive and prognostic markers for the outcome of chemotherapy in advanced colorectal cancer, a retrospective analysis of the phase III randomised CAIRO study.

We have tested several biomarkers [dihydropyrimidine dehydrogenase (DPD), orotate phosphoribosyl transferase (OPRT), thymidine phosphorylase (TP), thymidylate synthase (TS) and excision cross-complementing gene (ERCC1)] for their prognostic and predictive value in relation to the outcome of chemotherapy in tumour tissues of 556 advanced colorectal cancer (ACC) patients who were randomised between sequential treatment and combination treatment in the CApecitabine, IRinotecan, Oxaliplatin (CAIRO) study. DPD expression showed a statistically significant predictive value for combination treatment with capecitabine plus irinotecan with low versus high values resulting in an improved median progression-free survival (PFS) and median overall survival (OS) of 8.9 (95% confidence interval (CI) 8.3-9.9) versus 7.2 months (95% CI 6.5-8.1, p=0.006), and 21.5 months (95% CI 17.9-26.5) versus 16.9 months (95% CI 13.0-19.1, p=0.04), respectively. In the overall patient population a high OPRT expression in stromal cells was a favourable prognostic parameter for OS, with 21.5 months (95% CI 17.9-27.3) versus 17.2 months (95% CI 15.1-18.6, p=0.036), respectively. A similar effect was observed for PFS. In a multivariate analysis that included known prognostic factors these results remained significant and also showed that a high OPRT expression in tumour cells was an unfavourable prognostic parameter for PFS and OS. In conclusion, in this largest study on capecitabine with or without irinotecan to date we found a predictive value of DPD expression. Our results on the prognostic value of OPRT expression warrant further studies on the role of stromal cells in the outcome of treatments. The divergent results of ours and previous studies underscore the complexity of these biomarkers and currently prevent the routine use of these markers in daily clinical practice.

[Orotate phosphoribosyltransferase levels in gastric carcinoma and normal gastric mucosa - correlation with thymidylate synthase and dihydropyrimidine dehydrogenase levels and the changes after neoadjuvant chemotherapy].

Orotate phosphoribosyltransferase (OPRT, EC 2.4.2.10), a key enzyme that catalyzes one of the primary first-step phosphorylation processes of fluoropyrimidine, has recently been recognized as an important factor that primarily determines the anticancer effects of S-1. The OPRT levels were examined in 97 gastric carcinoma tissues and 65 normal gastric mucosa tissues obtained from patients with gastric carcinoma using a newly-developed enzyme-linked immunosorbent assay. Correlations with thymidylate synthase and dihydropyrimidine dehydrogenase levels and the effects of neoadjuvant chemotherapy were evaluated. The OPRT level in gastric carcinoma tissue was significantly higher than that in normal gastric mucosa. There was no correlation of OPRT level with either TS or DPD levels. There was no correlation of OPRT level between those in gastric carcinoma and those in normal gastric mucosa simultaneously obtained from identical patients. The OPRT levels in patients who underwent neoadjuvant chemotherapy were not different from those without neoadjuvant chemotherapy. These results suggest that activation of fluoropyrimidine mainly occurs in carcinoma tissues and the OPRT levels in carcinoma tissues were not influenced by neoadjuvant chemotherapy with fluoropyrimidine.

Modified Irinotecan/5FU/Leucovorin therapy in advanced colorectal cancer and predicting therapeutic efficacy by expression of tumor-related enzymes.

OBJECTIVE: To evaluate the efficacy and safety of a regimen using Irinotecan, 5FU and Leucovorin for patients with advanced or recurrent colorectal cancer. MATERIAL AND METHODS: Irinotecan (75 mg/m(2)) was administered biweekly, while 5FU (600 mg/m(2)) and Leucovorin (250 mg/m(2)) were administered weekly, for 6 weeks. RESULTS: The 21 consecutive patients subjected to this regimen showed a good response rate (43%) with minimal toxicity (incidence of grade 3/4: leukopenia and neutropenia, 5%, respectively, and vomiting, 10%). The mean survival time of all 21 patients was 15.7 months. This regimen could be a valid option for patients with advanced colorectal cancer, especially those seeking a good QoL (quality of life) for the remainder of their lives. We evaluated the expression of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP) and orotate phosphoribosyl transferase (OPRT) mRNAs, and sialyl Lewis X on formalin-fixed, paraffin-embedded colorectal tumor samples. Expression of TS mRNA or sialyl Lewis X was negatively correlated with the response from chemotherapy. Patients with low DPD mRNA expression in the tumor showed a significant longer survival than those with high expression. In patients with high TP mRNA expression, there was a tendency towards a high incidence of leukopenia. CONCLUSIONS: Some predictive factors elucidated in this study could contribute to the progress of the tumor-biology based, individualized chemotherapy for colorectal cancer patients.

Upregulation of enzymes metabolizing 5-fluorouracil in colorectal cancer.

BACKGROUND: The purpose of this study was to compare the activities of various enzymes, participating in the metabolism of 5-fluorouracil, between colorectal cancer and nontumor tissues and to investigate the association of the enzyme activities with clinicopathological backgrounds. METHODS: Activities of seven enzymes involved in nucleic acid metabolism--orotate phosphoribosyltransferase (OPRT), ribonucleotide reductase (RNR), thymidylate synthase, dihydropyrimidine dehydrogenase, thymidine phosphorylase, uridine phosphorylase and thymidine kinase (TK)--were measured in tumor and nontumor tissues from 28 patients who were operated on for colorectal cancers. RESULTS: OPRT, thymidylate synthase, RNR, thymidine phosphorylase, uridine phosphorylase and thymidine kinase activities were significantly higher in tumor areas than in nontumor areas. OPRT showed the highest T/N ratio (the ratio of each enzyme activity in tumor areas to that in nontumor areas). The T/N ratio of RNR activity showed a tendency to be associated with lymph node metastasis and Dukes classification. CONCLUSION: The results suggest that OPRT is a main enzyme participating in the phosphorylation of 5-fluorouracil and has an important role in tumor growth. The T/N ratio of RNR may be predictive of tumor progression.

Orotate phosphoribosyl transferase mRNA expression in oral squamous cell carcinoma and its relationship with the dihydropyrimidine dehydrogenase expression and the clinical effect of 5-fluorouracil.

In this study, we investigated whether orotate phosphoribosyl transferase (OPRT) correlates with the clinicopathological features and effect of 5-fluorouracil (5-FU) in human oral carcinoma. We examined the expression of OPRT mRNA by in situ hybridization in surgical specimens of oral squamous cell carcinoma. The expression of OPRT mRNA in oral carcinoma was observed in all specimens and such expression was higher than that seen in normal control tissue specimens. There was no correlation between the expression of OPRT mRNA and clinical factors, but the expression of OPRT mRNA was significantly associated with histological differentiation. The expression of OPRT mRNA showed correlation with effect of 5-FU for oral carcinoma in either in vivo or in vitro. These results suggest that the OPRT expressions may therefore be a prognostic factor of 5-FU efficacy in patients with oral squamous cell carcinoma.

Orotate phosphoribosyltransferase levels measured by a newly established enzyme-linked immunosorbent assay in gastric carcinoma.

A number of enzymes have been shown to be involved in the process of activation and/or degradation of 5-fluorouracil (5-FU), and are potential candidates for predicting chemosensitivity to 5-FU. Among these, orotate phosphoribosyltransferase (OPRT EC 2.4.2.10) is a key enzyme related to the first-step activation process of 5-FU and has been shown to be an important enzyme that helps to predict sensitivity to 5-FU and its related derivatives. We developed a new enzyme-linked immunosorbent assay (ELISA) to accurately assess intratumoral activity of OPRT. A new sandwich ELISA was established using anti-OPRT polyclonal antibodies obtained from the rabbit immunized with the recombinant human peptides of the OPRT molecule. OPRT levels were measured in eight human cancer xenografts and in 75 gastric cancer tissues using both a newly established ELISA and a conventional enzyme assay, using radiolabeled 5-FU as a substrate. There was a significant correlation between OPRT levels measured by this ELISA and OPRT enzyme activity the in eight human cancer xenografts (r2 = 0.782) and gastric carcinoma tissue (r2 = 0.617). The ELISA system for OPRT requires a minimal amount of carcinoma tissue, making it an easy-to-use assay system to predict sensitivity to 5-FU and its derivatives in gastric carcinoma. There was a significant correlation between tumor growth inhibition rates against the oral administration of oral-uracil/tegafur (UFT) and OPRT enzyme activity in the human cancer xenografts (r2 = 0.574). These results suggest that this newly developed sandwich ELISA system for the quantification of OPRT levels is technically simple, feasible and a useful tool to predict sensitivity to fluoropyrimidine-based anticancer chemotherapy in patients with gastric carcinoma and other cancers.

[Clinicopathological significance of orotate phosphoribosyltransferase in gastric carcinoma].

Orotate phosphoribosyltransferase (OPRT EC 2.4.2.10) is a key enzyme related to the first-step phosphorylation process of 5-fluorouracil. We have recently developed an ELISA system to measure OPRT levels in cancerous tissues. We examined OPRT levels in 75 gastric carcinoma tissues using this ELISA, and the relationships with clinicopathologic factors were evaluated. A total of 75 surgically-resected gastric carcinoma tissues were subjected to the present study. The intratumoral OPRT level was determined by a newly-developed enzyme-linked immunosorbent assay (ELISA). Enzyme activities of OPRT were also determined using a conventional enzyme assay using radiolabeled 5-fluorouracil as a substrate. OPRT levels in gastric carcinoma tissues measured by ELISA were 5.4+/-3.6 ng/mg protein, ranging from 0.2 to 15.7 ng/mg protein. There was a significant correlation between the OPRT level measured by the ELISA and OPRT enzyme activity (y=0.545x - 0.017, r(2)=0.617, p<0.0001). OPRT levels were significantly higher in patients with differentiated type and invasive type of gastric carcinoma, whereas OPRT levels were not associated with the pathological stage of gastric carcinoma. These results suggest that OPRT levels were related to the histopathological characteristics of gastric carcinoma, and may be related to the response to fluoropyrimidine-based anticancer chemotherapy.

Predicting 5-fluorouracil chemosensitivity of liver metastases from colorectal cancer using primary tumor specimens: three-gene expression model predicts clinical response.

We identified genes related to 5-fluorouracil (5-FU) sensitivity in colorectal cancer and utilized these genes for predicting the 5-FU sensitivity of liver metastases. Eighty-one candidate genes involved in 5-FU resistance in gastric and colon cancer cell lines were previously identified using a cDNA microarray. In this study, the mRNA expression levels of these 81 selected genes and the genes of 5-FU-related enzymes, including thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD) and orotate phosphoribosyltransferase (OPRT), were measured using real-time quantitative RT-PCR assays of surgically resected materials from primary colorectal tumors in 22 patients. Clinical responses were estimated by evaluating the effects of 5-FU-based hepatic artery injection (HAI) chemotherapy for synchronous liver metastases. Four genes (TNFRSF1B, SLC35F5, NAG-1 and OPRT) had significantly different expression profiles in 5-FU-nonresponding and responding tumors (p < 0.05). A "Response Index" system using three genes (TNFRSF1B, SLC35F5 and OPRT) was then developed using a discriminate analysis; the results were well correlated with the individual chemosensitivities. Among the 11 cases with positive scores in our response index, 9 achieved a reduction in their liver metastases after 5-FU-based chemotherapy, whereas only 1 of the 11 cases with negative scores responded well to chemotherapy. Our "Response Index" system, consisting of TNFRSF1B, SLC35F5 and OPRT, has great potential for predicting the efficacy of 5-FU-based chemotherapy against liver metastases from colorectal cancer.

Prognostic impact of orotate phosphoribosyl transferase among 5-fluorouracil metabolic enzymes in resectable colorectal cancers treated by oral 5-fluorouracil-based adjuvant chemotherapy.

Orotate phosphoribosyl transferase (OPRT) is the main enzyme that involves in phosphoribosylation of 5-fluorouracil (5-FU), an essential step that leads to tumor growth inhibition. In our study, the prognostic relevance of OPRT, thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) in resectable colorectal cancer (CRC) patients treated by oral 5-FU were compared to further clarify the prognostic value of OPRT. Tumor tissue was collected from 90 CRC patients and the patients were followed for 5.2 years (Median). TS, DPD and OPRT activities in the extract of tumor tissue were determined enzymatically. The cut-off value of OPRT (0.147 nmol/(min mg), TS (0.044 pmol/mg) and DPD (72.10 pmol/(min mg) were determined by maximal chi(2) method. Among these 5-FU metabolic enzymes, only high OPRT group demonstrated significantly better disease-free survival (DFS) (p = 0.0152) and better overall survival (p = 0.0078). In Cox regression analysis, node status (p < 0.0005) and OPRT (p = 0.044) were significant factors for DFS. OPRT activity in tumor tissue was a predictor of prognosis in resectable CRC patients treated by oral 5-FU-based adjuvant chemotherapy, and was useful to pick-up high risk patients independent from known prognosis factors.

Both gene expression for orotate phosphoribosyltransferase and its ratio to dihydropyrimidine dehydrogenase influence outcome following fluoropyrimidine-based chemotherapy for metastatic colorectal cancer.

Activation of 5-fluorouracil into its nucleotides requires phosphorylation by three pathways involving orotate phosphoribosyl-transferase (OPRT), uridine phosphorylase (UP), or thymidine phosphorylase (TP). In this study, we investigated the association between gene expressions of these three enzymes and antitumour effect. Gene expressions in primary colorectal tumours were analysed by a real-time reverse transcriptional-polymerase chain reaction method in 37 patients receiving oral treatment of tegafur-uracil and leucovorin for metastatic diseases. The median values of OPRT mRNA expressions were 1.39 and 0.85 for responding tumours and nonresponding tumours, respectively, showing a statistically significant difference (P=0.0008). Responding tumours had statistically lower expressions of TP mRNA than nonresponding tumours (P=0.006). However, there was no difference in UP mRNA expression between responding and nonresponding tumours. Patients with high OPRT (>/=1.0) gene expression survived longer than those with low OPRT (<1.0) expression. Dihydropyrimidine dehydrogenase (DPD) gene expressions were measured. Responding tumours had a statistically higher OPRT/DPD ratio than the nonresponding ones (P=0.003). When the median value of the OPRT/DPD ratio was selected as the cutoff value, patients with a high OPRT/DPD ratio survived statistically longer than those with a low ratio (P=0.0014). In conclusion, both the expression of OPRT gene and the OPRT/DPD ratio might be useful as predictive parameters for the efficacy of fluoropyrimidine-based chemotherapy for metastatic colorectal cancer.

Relationships between the expression of thymidylate synthase, dihydropyrimidine dehydrogenase, and orotate phosphoribosyltransferase and cell proliferative activity and 5-fluorouracil sensitivity in colorectal carcinoma.

BACKGROUND: The site of action of the 5-fluorouracil (5-FU) antitumor effect has been explicated in recent years. Many studies have investigated enzymes involved in 5-FU metabolism in attempts to predict this effect, and a correlation of enzyme activity with the 5-FU drug sensitivity test has been reported. The aim of this study was to identify the biochemical response determinants of 5-FU. Additionally, we aimed to clarify the association between cell proliferative activity and the response to 5-FU of colorectal cancer. METHODS: Our research subjects were 54 patients with colorectal carcinoma who had undergone operations between August 1999 and July 2001 in our department. Assays of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and orotate phosphoribosyltransferase (OPRT) activities in colorectal carcinoma tissue and assays of 5-FU sensitivity by the collagen gel droplet embedded culture drug sensitivity test (CD-DST) were conducted to investigate the relationships between each enzyme activity and 5-FU sensitivity. In addition, the proliferative activity of cancer cells was evaluated with Ki-67 antibody, and the relationship of this activity to each enzyme activity and 5-FU sensitivity were investigated. RESULTS: 5-FU sensitivity was high in the low-TS-activity group and in the high-OPRT-activity group. Cancers with high cell proliferative activity showed good sensitivity to 5-FU, and TS and OPRT activities were high in such cancers. CONCLUSION: The results suggest that OPRT activity can predict sensitivity to 5-FU, and high OPRT activity may cause good 5-FU sensitivity in cancers with high cell proliferative activity.

Predicting 5-FU sensitivity using human colorectal cancer specimens: comparison of tumor dihydropyrimidine dehydrogenase and orotate phosphoribosyl transferase activities with in vitro chemosensitivity to 5-FU.

BACKGROUND: In tumor cells, the enzyme orotate phosphoribosyl transferase (OPRT) contributes to 5-fluorouracil (5-FU) phosphorylation and another enzyme, dihydropyrimidine dehydrogenase (DPD), is associated with 5-FU catabolic action. We measured OPRT and DPD activities and, to determine whether their levels might serve as indicators of 5-FU sensitivity, simultaneously assayed in vitro chemosensitivity to 5-FU. METHODS: Tissue specimens were obtained from colorectal cancer patients and in vitro chemosensitivity was tested using fluorescein diacetate assay (FDA) or histoculture drug response assay (HDRA). DPD and OPRT activities were measured by radioassay. RESULTS: The chemosensitivity assay was performed on 62 colorectal cancer specimens. Results were evaluable in 29 of 30 cases (96.7%) for FDA and 30 of 32 cases (98.3%) for HDRA. The positive sensitivity rate was 37.9% by FDA assay and 30% by HDRA assay. In positive specimens, the mean DPD activity was 44.9 +/- 32.6 pmol/min per mg protein, and in negative specimens, it was 53.8 +/- 33.7 pmol/min per mg protein ( P= 0.875). In contrast, the mean OPRT value was significantly higher in positive specimens (0.418 +/- 0.180 nmol/min per mg protein) than in negative specimens (0.325 +/- 0.153 nmol/min per mg protein; P < 0.05). The chemosensitivity test proved positive in 60% of the specimens with ORPT activity of 0.413 or above and 50% of those with DPD activity of 30 or below. Of the patient specimens showing OPRT activity of 0.413 or above and DPD activity of 30 or below, 88.9% were positive for 5-FU sensitivity, suggesting the possibility that the combination of these two levels may be predictive of 5-FU positive sensitivity. CONCLUSION: DPD and OPRT activities within cancer cells may predict positive sensitivity to 5-FU.

Control of pyrimidine synthesis in Pseudomonas fragi.

AIMS: To study the regulation of the de novo pyrimidine biosynthetic enzymes in the food-spoilage agent Pseudomonas fragi ATCC 4973. METHODS AND RESULTS: The de novo pyrimidine biosynthetic enzymes were measured in extracts of Ps. fragi ATCC 4973 cells and of cells from auxotrophs deficient for dihydroorotase or OMP decarboxylase activity. Pyrimidine biosynthetic enzyme activities in ATCC 4973 were influenced by pyrimidine supplementation to the culture medium. The pyrimidine limitation of each auxotroph elevated the de novo enzyme activities, indicating that this pathway may be repressible by a pyrimidine-related compound. Aspartate transcarbamoylase activity in ATCC 4973 was inhibited in vitro by pyrophosphate and purine or pyrimidine nucleotides. CONCLUSIONS: Pyrimidine synthesis in Ps. fragi appeared to be controlled at the transcriptional level and at the level of activity for aspartate transcarbamoylase. Its transcriptional regulation seemed to be more highly controlled than what was observed in the closely related species Pseudomonas putida and Pseudomonas fluorescens. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates that pyrimidine synthesis is regulated in Ps. fragi. This could prove useful to future studies examining its biological control and its taxonomic assignment.

Detection and location of the enzymes of de novo pyrimidine biosynthesis in mammalian spermatozoa.

Enzymes of the pathway for de novo biosynthesis of pyrimidine nucleotides have been reported in spermatozoa from fruitfly and mammals. The aim of the present study was to test the hypothesis that the enzymes for biosynthesis of uridine monophosphate (UMP) are concentrated near the mitochondria, which are segregated in the mid-piece of spermatozoa. Baby hamster kidney fibroblasts were compared with spermatozoa from rams, boars, bulls and men. Antibodies raised against synthetic peptides from sequences of the multienzyme polypeptides containing glutamine-dependent carbamyl phosphate synthetase, aspartate transcarbamylase and dihydroorotase (CAD) and UMP synthase, which catalyse reactions 1-3 and 5-6, respectively, were used, together with an affinity-purified antibody raised against dihydroorotate dehydrogenase (DHODH), the mitochondrial enzyme for step 4. Western blot analysis, immunofluorescent microscopy and immunoelectron microscopy confirmed that CAD and UMP synthase are found in the cytoplasm around and outside the mitochondria; DHODH is found exclusively inside the mitochondria. CAD was also located in the nucleus, where it has been reported in the nuclear matrix, and in the cytoplasm, apparently associated with the cytoskeleton. It is possible that CAD in the cytoplasm has a role unconnected with pyrimidine biosynthesis.

Control of pyrimidine formation in Pseudomonas putida ATCC 17536.

The regulation of de novo pyrimidine biosynthesis in Pseudomonas putida ATCC 17536 by pyrimidines was explored. The pathway enzyme activities were higher in glucose-grown cells than in succinate-grown cells, indicating catabolite repression by succinate. In P. putida cells grown on succinate as a carbon source, only aspartate transcarbamoylase activity was greatly diminished by uracil supplementation. When glucose was the carbon source, orotic acid supplementation significantly decreased orotate phosphoribosyltransferase and orotidine 5'-monophosphate (OMP) decarboxylase activities. Uracil auxotrophs, deficient for dihydroorotase activity or with reduced phosphoribosyltransferase activity, were isolated. After pyrimidine limitation of both auxotrophs, the greatest derepression of enzyme activity was observed for OMP decarboxylase independent of carbon source. Orotic acid induced both phosphoribosyltransferase and decarboxylase activities in glucose-grown cells of the dihydroorotase-deficient strain. Regulation at the transcriptional level of de novo pyrimidine biosynthetic enzyme synthesis in P. putida ATCC 17536 was observed, which contrasts with previous observations.

A nonradioactive high-performance liquid chromatographic microassay for uridine 5'-monophosphate synthase, orotate phosphoribosyltransferase, and orotidine 5'-monophosphate decarboxylase.

A novel nonradioactive, microassay method has been developed to determine simultaneously the two enzymatic activities of orotate phosphoribosyltransferase (OPRTase) and orotidine 5'-monophosphate decarboxylase (ODCase), either as a bifunctional protein (uridine 5'-monophosphate synthase, UMPS) or as separate enzymes. Substrates (orotate for OPRTase or orotidine 5'-monophosphate for ODCase) and a product (UMP) of the enzymatic assay were separated by high-performance liquid chromatography (HPLC) using a reversed-phase column and an ion-pairing system; the amount of UMP was quantified by dual-wavelength uv detection at 260 and 278 nm. This HPLC assay can easily detect picomole levels of UMP in enzymatic reactions using low specific activity UMPS of mammalian cell extracts, which is difficult to do with the other nonradioactive assays that have been described. The HPLC assay is suitable for use in protein purification and for kinetic study of these enzymes.