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1.
J Med Invest ; 70(3.4): 503-507, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37940539

RESUMO

Paragangliomas are neural-crest-derived nonepithelial neuroendocrine tumors distributed along the parasympathetic and sympathetic nerves. To our knowledge, no studies were reported regarding sinus arrest on day 4 after paraganglioma resection. A 66-year-old female patient with a history of pulmonary vein isolation visited our department for sigmoid colon cancer treatment. Enhanced computed tomography revealed an enhanced small nodule-like lymph node near the root of the inferior mesenteric artery. The patient underwent laparoscopic colectomy with regional lymph node dissection. Postoperatively, paroxysmal atrial fibrillation attacks developed, and the patient resumed oral medication. Additionally, sinus arrest after tachycardia developed. Changing the oral medication could maintain her circulatory dynamics. Pathological examination revealed that differentiated tubular adenocarcinoma infiltrated the submucosa. Immunohistochemically, the excised nodule as a lymph node was considered a functional paraganglioma. Our case indicates that paraganglioma resection and oral medication resumption may contribute to sinus arrest. When arrhythmias affecting the circulation occur perioperatively, the presence of a catecholamine-producing tumor should be considered in addition to cardiac disease. J. Med. Invest. 70 : 503-507, August, 2023.


Assuntos
Excisão de Linfonodo , Paraganglioma , Humanos , Feminino , Idoso , Excisão de Linfonodo/métodos , Tomografia Computadorizada por Raios X , Paraganglioma/diagnóstico por imagem , Paraganglioma/cirurgia
2.
Prostate ; 83(6): 563-571, 2023 05.
Artigo em Inglês | MEDLINE | ID: mdl-36661102

RESUMO

PURPOSE: We aimed to assess the oncologic efficacy of combining docetaxel (DOC) versus abiraterone (ABI) with androgen deprivation therapy (ADT) in patients with high-risk metastatic hormone-sensitive prostate cancer (mHSPC), with a focus on the efficacy of sequential therapy, in a real-world clinical practice setting. METHODS: The records of 336 patients who harbored de novo high-risk mHSPC, based on the LATITUDE criteria, and had received ADT with either DOC (n = 109) or ABI (n = 227) were retrospectively analyzed. Overall survival (OS), cancer-specific survival (CSS), progression-free survival (PFS), including time to castration-resistant prostate cancer (CRPC), time to 2nd-line progression (PFS2), and 2nd- and 3rd-line PFS, were compared. We used one-to-two propensity score matching to minimize the confounders. The differential efficacy of 2nd-line therapy based on agents in each arm was evaluated using the unmatched cohort as an additional interest. RESULTS: After propensity score matching, 86 patients treated with DOC + ADT and 172 with ABI + ADT were available for analyses. The 3-year OS and CSS for DOC versus ABI were 76.2% versus 75.1% (p = 0.8) and 78.2% versus 78.6% (p = 1), respectively. There was no difference in the median PFS2 (49 vs. 43 months, p = 0.39), while the median time to CRPC in patients treated with ABI was significantly longer compared to those treated with DOC (42 vs. 22 months; p = 0.006). The median 2nd-line PFS (14 vs. 4 months, p < 0.001) and 3rd-line PFS (4 vs. 2 months, p = 0.012) were significantly better in the DOC group than in the ABI group. Among the unmatched cohort, after ABI for mHSPC, the median 2nd-line PFS did not differ between the patients treated with DOC and those treated with enzalutamide as 2nd-line therapy (both 3 months, p = 0.8). CONCLUSIONS: ADT with DOC or ABI has comparable oncologic outcomes in terms of OS, CSS, and PFS2 in patients with de novo high-risk mHSPC. Compared to DOC, ABI resulted in longer time to CRPC but worse 2nd and 3rd-line PFS. Further studies are needed to clarify the optimal sequence of therapy in the upfront intensive treatment era.


Assuntos
Neoplasias de Próstata Resistentes à Castração , Neoplasias da Próstata , Masculino , Humanos , Docetaxel/uso terapêutico , Neoplasias da Próstata/patologia , Neoplasias de Próstata Resistentes à Castração/patologia , Antagonistas de Androgênios/uso terapêutico , Estudos Retrospectivos , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Hormônios/uso terapêutico , Resultado do Tratamento
3.
World J Urol ; 41(8): 2051-2062, 2023 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-35596809

RESUMO

PURPOSE: The aim of this study was to investigate the oncologic efficacy of combining docetaxel with androgen deprivation therapy (ADT) versus nonsteroidal antiandrogen (NSAA) with ADT in patients with high-volume metastatic hormone-sensitive prostate cancer (mHSPC) with focus on the effect of sequential therapy in a real-world clinical practice setting. METHODS: The records of 382 patients who harbored high-volume mHSPC, based on the CHAARTED criteria, and had received ADT with either docetaxel (n = 92) or NSAA (bicalutamide) (n = 290) were retrospectively analyzed. The cohorts were matched by one-to-one propensity scores based on patient demographics. Overall survival (OS), cancer-specific survival (CSS), progression-free survival (PFS), including time to castration-resistant prostate cancer (CRPC), and time to second-line progression (PFS2) were compared. 2nd-line PFS defined as the time from CRPC diagnosis to progression after second-line therapy was also compared. RESULTS: After matching, a total of 170 patients were retained: 85 patients treated with docetaxel + ADT and 85 patients treated with NSAA + ADT. The median OS and CSS for docetaxel + ADT versus NSAA + ADT were not reached (NR) vs. 49 months (p = 0.02) and NR vs. 55 months (p = 0.02), respectively. Median time to CRPC and PFS2 in patients treated with docetaxel + ADT was significantly longer compared to those treated with NSAA (22 vs. 12 months; p = 0.003 and, NR vs. 28 months; p < 0.001, respectively). There was no significant difference in 2nd-line PFS between the two groups. CONCLUSIONS: Our analysis suggested that ADT with docetaxel significantly prolonged OS and CSS owing to a better time to CRPC and PFS2 in comparison to NSAA + ADT in high-volume mHSPC.


Assuntos
Drogas Antiandrogênicas não Esteroides , Neoplasias de Próstata Resistentes à Castração , Neoplasias da Próstata , Masculino , Humanos , Docetaxel/uso terapêutico , Neoplasias da Próstata/patologia , Antagonistas de Androgênios/uso terapêutico , Drogas Antiandrogênicas não Esteroides/uso terapêutico , Androgênios/uso terapêutico , Neoplasias de Próstata Resistentes à Castração/patologia , Estudos Retrospectivos , Pontuação de Propensão , Resultado do Tratamento , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico
4.
Surg Case Rep ; 8(1): 112, 2022 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-35699804

RESUMO

BACKGROUND: Falciform ligament abscess (FLA) is a rare disease, and its diagnosis can be challenging without typical image findings of an abscess. We report a patient with FLA that presented as a mass, with an indistinct border between it and the liver, in addition to disseminated foci within the liver. This made it difficult to determine whether it was FLA or a malignancy. CASE PRESENTATION: A 69-year-old man presented with epigastric pain. Contrast-enhanced computed tomography revealed a 25-mm mass below the middle of the diaphragm. Based on an initial diagnosis of infection of the falciform ligament, we administered conservative antibiotic treatment and there was initial improvement in the patient's clinical condition and laboratory data. However, he continued to experience mild epigastric pain. A month later, imaging studies revealed enlargement of the falciform ligament mass and the emergence of a new nodule in the liver, whereas laboratory findings showed re-elevated C-reactive protein levels. Since conservative treatment had failed, we decided to perform surgery. Considering the imaging study findings, malignant disease could not be ruled out. Based on the operative findings, we performed combined resection of the falciform ligament, left liver, and gallbladder. Histopathological examination of the resected specimens revealed extensive neutrophil infiltration and the presence of giant cells and foam cells within the lesions. These findings were indicative of abscess. Pseudomonas aeruginosa was cultured from the pus in the falciform ligament mass and bile in the gallbladder. Although multiple abscesses postoperatively developed in the residual portion of the liver, they could be treated through antibiotic therapy. CONCLUSIONS: FLA can spread to both adjacent and distant organs via its rich vascular and lymphatic networks. When FLA displays atypical image findings and/or an atypical clinical course, it can be difficult to distinguish it from malignant disease. In such cases, surgical treatment, with intraoperative pathological diagnosis, should be attempted.

5.
Prostate ; 82(1): 3-12, 2022 01.
Artigo em Inglês | MEDLINE | ID: mdl-34559410

RESUMO

BACKGROUND: Although prostate cancer is a very common form of malignancy in men, the clinical significance of androgen deprivation therapy (ADT) with abiraterone acetate versus the nonsteroidal antiandrogen bicalutamide has not yet been verified in patients with high-risk metastatic hormone-sensitive prostate cancer (mHSPC). The present study was designed to initiate this verification in real-world Japanese clinical practice. METHODS: We retrospectively analyzed the records of 312 patients with high-risk mHSPC based on LATITUDE criteria and had received ADT with bicalutamide (n = 212) or abiraterone acetate (n = 100) between September 2015 and December 2020. Bicalutamide was given at 80 mg daily and abiraterone was given at 1000 mg daily as four 250-mg tablets plus prednisolone (5-10 mg daily). Overall survival (OS), cancer-specific survival (CSS), and time to castration-resistant prostate cancer (CRPC) were compared. The prognostic factor for time to CRPC was analyzed by Cox proportional hazard model. RESULTS: Patients in the bicalutamide group were older, and more of them had poor performance status (≧2), than in the abiraterone group. Impaired liver function was noted in 2% of the bicalutamide group and 16% of the abiraterone group (p < 0.001). Median follow-up was 22.5 months for bicalutamide and 17 months for abiraterone (p < 0.001). Two-year OS and CSS for bicalutamide versus abiraterone was 77.8% versus 79.5% (p = 0.793) and 81.1% versus 82.5% (p = 0.698), respectively. Median time to CRPC was significantly longer in the abiraterone group than in the bicalutamide group (NA vs. 13 months, p < 0.001). In multivariate analysis, Gleason score ≧9, high alkaline phosphatase, high lactate dehydrogenase, liver metastasis, and bicalutamide were independent prognostic risk factors for time to CRPC. Abiraterone prolonged the time to CRPC in patients with each of these prognostic factors. CONCLUSIONS: Despite limitations regarding the time-dependent bias, ADT with abiraterone acetate significantly prolonged the time to CRPC compared to bicalutamide in patients with high-risk mHSPC. However, further study with longer follow-up is needed.


Assuntos
Acetato de Abiraterona , Anilidas , Neoplasias Hepáticas , Nitrilas , Prednisolona , Neoplasias de Próstata Resistentes à Castração , Neoplasias da Próstata , Compostos de Tosil , Acetato de Abiraterona/administração & dosagem , Acetato de Abiraterona/efeitos adversos , Antagonistas de Androgênios/administração & dosagem , Antagonistas de Androgênios/efeitos adversos , Anilidas/administração & dosagem , Anilidas/efeitos adversos , Protocolos de Quimioterapia Combinada Antineoplásica , Pesquisa Comparativa da Efetividade , Humanos , Japão/epidemiologia , Testes de Função Hepática/métodos , Neoplasias Hepáticas/diagnóstico , Neoplasias Hepáticas/secundário , Masculino , Pessoa de Meia-Idade , Gradação de Tumores , Estadiamento de Neoplasias , Nitrilas/administração & dosagem , Nitrilas/efeitos adversos , Drogas Antiandrogênicas não Esteroides/administração & dosagem , Drogas Antiandrogênicas não Esteroides/efeitos adversos , Prednisolona/administração & dosagem , Prednisolona/efeitos adversos , Prognóstico , Neoplasias da Próstata/tratamento farmacológico , Neoplasias da Próstata/epidemiologia , Neoplasias da Próstata/patologia , Neoplasias de Próstata Resistentes à Castração/diagnóstico , Neoplasias de Próstata Resistentes à Castração/epidemiologia , Neoplasias de Próstata Resistentes à Castração/etiologia , Estudos Retrospectivos , Medição de Risco/métodos , Compostos de Tosil/administração & dosagem , Compostos de Tosil/efeitos adversos
6.
Gan To Kagaku Ryoho ; 48(6): 825-827, 2021 Jun.
Artigo em Japonês | MEDLINE | ID: mdl-34139732

RESUMO

Chemotherapy is the standard treatment for unresectable gastric cancer, but there is no clear evidence of therapeutic lymphadenectomy in conversion surgery after the tumor shrinks or the combined effect of perioperative chemotherapy. A 63-year-old man was diagnosed with advanced gastric cancer by upper gastrointestinal endoscopy; computed tomography (CT)showed swelling of the gastric regional lymph nodes, abdominal para-aortic lymph nodes, and left supraclavicular lymph node. After 4 courses of combination therapy with S-1 and cisplatin(SP therapy), CT showed that the left supraclavicular lymph node disappeared and the para-aortic lymph node was reduced. Distal gastrectomy and D2 plus para-aortic lymph node dissection were performed as conversion surgery. Two courses of postoperative SP therapy were administered, and S-1 monotherapy was continued for 2 years and 6 months. After 5 years and 1 month since the operation, the patient is alive without recurrence. This case shows that SP therapy can be effective as chemotherapy for unresectable gastric cancer. In addition, that conversion surgery after chemotherapy may contribute to recurrence-free survival.


Assuntos
Neoplasias Gástricas , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Gastrectomia , Humanos , Excisão de Linfonodo , Linfonodos , Metástase Linfática , Masculino , Pessoa de Meia-Idade , Recidiva Local de Neoplasia , Neoplasias Gástricas/tratamento farmacológico , Neoplasias Gástricas/cirurgia
7.
Surg Case Rep ; 6(1): 228, 2020 Sep 29.
Artigo em Inglês | MEDLINE | ID: mdl-32990830

RESUMO

BACKGROUND: Pancreaticoduodenectomy (PD) is rarely performed for pancreatic cancer with hepatic arterial invasion owing to its poor prognosis and high surgical risks. Although there has been a recent increase in the reports of PD combined with hepatic arterial resection due to improvements in disease prognosis and operative safety, PD with major arterial resection and reconstruction is still considered a challenging treatment. CASE PRESENTATION: A 61-year-old man with back pain was diagnosed with pancreatic head and body cancer. Although distant metastasis was not confirmed, the tumor had extensively invaded the hepatic artery; therefore, we diagnosed the patient with locally advanced unresectable pancreatic cancer. After gemcitabine plus nab-paclitaxel (GnP) therapy, the tumor considerably decreased in size from 35 to 20 mm. Magnetic resonance imaging revealed a gap between the tumor and the hepatic artery. Tumor marker levels returned to their normal range, and we decided to perform conversion surgery. In this case, an artery of liver segment 2 (A2) had branched from the left gastric artery; therefore, we decided to preserve A2 and perform PD combined with hepatic arterial resection without reconstruction. After four cycles of GnP therapy, we performed hepatic arterial embolization to prevent postoperative ischemic complications prior to surgery. Immediately after embolization, collateral arterial blood flow to the liver was observed. Operation was performed 19 days after embolization. Although there was a temporary increase in liver enzyme levels and an ischemic region was found near the surface of segment 8 of the liver after surgery, no liver abscess developed. The postoperative course was uneventful, and S-1 was administered for a year as adjuvant chemotherapy. The patient is currently alive without any ischemic liver events and cholangitis and has not experienced recurrence in the past 4 years since the surgery. CONCLUSIONS: In PD for pancreatic cancer with hepatic arterial invasion, if a part of the hepatic artery is aberrant and can be preserved, combined resection of the common and proper hepatic artery without reconstruction might be feasible for both curability and safety.

13.
Asian J Endosc Surg ; 10(1): 23-27, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27515772

RESUMO

INTRODUCTION: Complete mesocolic excision is currently recognized as a standard procedure for colon cancer. Gastroepiploic, infrapyloric, and superficial pancreatic head lymph node metastases in the gastrocolic ligament have been reported for colon cancer close to the hepatic flexure. We sought to investigate metastases in the gastrocolic ligament in colon cancer close to the hepatic flexure. METHODS: This was a single-center retrospective study. All patients with T2 or deeper invasive colon cancer in the relevant tumor location who underwent laparoscopic right hemicolectomy or extended right hemicolectomy at our institution between 1 April 2011 and 31 March 2015 were included. RESULTS: Lymph node dissection in the gastrocolic ligament was performed in 35 cases. Complications occurred in 11 patients (31%) and were grades I and II according to the Clavien-Dindo classification. Lymph node metastases in the gastrocolic ligament were found in only three patients (9%). Each metastasis was larger than 9 mm. CONCLUSIONS: Metastases in the gastrocolic ligament occurred in 9% of patients with T2 or deeper invasive colon cancer close to the hepatic flexure. Laparoscopy was feasible and useful during gastrocolic ligament resection. This study included a small sample and lacked an extended follow-up. Further studies are needed to determine the clinical relevance of this finding, particularly in terms of recurrence and long-term survival.


Assuntos
Colectomia , Neoplasias do Colo/cirurgia , Laparoscopia , Excisão de Linfonodo/métodos , Linfonodos/patologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Colo Ascendente , Neoplasias do Colo/patologia , Feminino , Seguimentos , Humanos , Ligamentos , Linfonodos/cirurgia , Metástase Linfática , Masculino , Pessoa de Meia-Idade , Invasividade Neoplásica , Estadiamento de Neoplasias , Estudos Retrospectivos
14.
Gan To Kagaku Ryoho ; 42(11): 1435-7, 2015 Nov.
Artigo em Japonês | MEDLINE | ID: mdl-26602407

RESUMO

The patient was a 68-year-old male who had bloody stools. A colonoscopy revealed a sigmoid colon stricture, and a histological examination confirmed the presence of a poorly differentiated adenocarcinoma.Computed tomography revealed the involvement of a para-aortic lymph nodes, without other metastatic lesions. The patient underwent a sigmoidectomy (with regional lymph node dissection) and a para-aortic lymph node biopsy to prove the histological conformation. Subsequently, he was provided with 6 courses of modified FOLFOX6(mFOLFOX6) chemotherapy, resulting in a marked decrease in para-aortic lymph node involvement. He subsequently underwent a para-aortic lymphadenectomy. The resected specimen was mostly composed of fibrous degenerative tissue; viable cancer cells were observed only in a 2-mm² area. The patient was provided with 6 more courses of mFOLFOX6 chemotherapy, and has since been free of recurrence (for 6 years and 1 month after the second surgery).


Assuntos
Adenocarcinoma/tratamento farmacológico , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Excisão de Linfonodo , Neoplasias do Colo Sigmoide/tratamento farmacológico , Adenocarcinoma/cirurgia , Idoso , Aorta/patologia , Quimioterapia Adjuvante , Fluoruracila/uso terapêutico , Humanos , Leucovorina/uso terapêutico , Masculino , Compostos Organoplatínicos/uso terapêutico , Recidiva , Neoplasias do Colo Sigmoide/patologia , Neoplasias do Colo Sigmoide/cirurgia , Tomografia Computadorizada por Raios X , Resultado do Tratamento
15.
Dis Colon Rectum ; 55(12): 1295-9, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23135589

RESUMO

BACKGROUND: Only a limited number of instruments can be used in single-access laparoscopic colectomy, and triangulation must be forfeited to avoid instrument collision. We investigated whether this problem could be overcome by performing laparoscopic colectomy by the use of the lateral decubitus position, making full use of gravity. OBJECTIVE: The aim of this study was to determine whether single-access laparoscopic colectomy could be achieved while maintaining patients in the lateral decubitus position. DESIGN: This was a prospective study. SETTING: This single-center study was conducted in a hospital. PATIENTS: Ten consecutive patients (4 men and 6 women) with stage II or III colon cancer were included. INTERVENTIONS: Each patient was placed in the lateral decubitus position. Single-port access to the abdomen was provided by a 3.0-cm incision at the umbilicus. The roots of the supplying or draining vessels were isolated and divided for lymphadenectomy. Next, the colon was dissected from a lateral approach, without the help of the assistant. The specimen was extracted from the single-access incision. Extracorporeal or intracorporeal anastomosis was performed. MAIN OUTCOME MEASURES: The primary outcome measured was the feasibility of single-access laparoscopic colectomy in the lateral decubitus position. RESULTS: There were no intraoperative complications and no need for conversions to conventional laparoscopic surgery, open surgery, or the supine position. The median total surgical time was 154 minutes (interquartile range, 135-220 minutes). Surgical blood loss was slight (<20 mL) in all patients. No postoperative complications occurred. The median postoperative hospital stay was 7 days (interquartile range, 5-7 days). LIMITATIONS: The sample size was small. CONCLUSIONS: Our results show that single-access laparoscopic colectomy in the lateral decubitus position is safe and feasible.


Assuntos
Colectomia/métodos , Neoplasias do Colo/cirurgia , Laparoscopia/métodos , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Tempo de Internação/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Posicionamento do Paciente , Estudos Prospectivos , Resultado do Tratamento
16.
Dis Colon Rectum ; 55(7): 815-20, 2012 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-22706136

RESUMO

BACKGROUND: In single-access laparoscopic colectomy, the number of instruments that can be inserted through the single-access site is limited by instrument collision. To compensate, triangulation is necessary, but the operative field becomes inadequate. To overcome this problem, intracorporeal attachable and detachable instruments can broaden the field of visceral tissue by retracting from at least 2 points. OBJECTIVE: We tested this new procedure for colon cancer surgery. DESIGN: This is a prospective study. SETTING: This study was conducted at a single-center hospital. PATIENTS: Ten consecutive patients (3 male and 7 female) with stage II or III colon cancer underwent the procedure. INTERVENTIONS: All patients received a 3.0-cm incision at the umbilicus or right iliac fossa. At least 2 clips and a suspending bar were inserted through a 12-mm port in a multiport access device. The clips grasped the mesocolon at different points and were retracted with either an extracorporeal magnet or fine-loop retractors; this broadened the operative field in the mesocolon by at least 2 points. The mesocolon was dissected with a medial to lateral approach. The suspended bar was tied to 2 fine-loop retractors and manipulated to enlarge the operative field in the mesocolon. The roots of the vascular pedicles were isolated and divided during lymph node dissection. After extracting the specimen, an anastomosis was performed. MAIN OUTCOME MEASURES: Intra- and postoperative complications due to inadequate access were the primary outcomes measured. RESULTS: There were no intraoperative complications and no need for conversions to open surgery or second access ports. The median total surgical time was 182 minutes (range, 122-245). Surgical blood loss was slight (range, 1-20 mL) in all patients. No postoperative complications occurred. The postoperative hospital stay was 5 to 7 days. LIMITATIONS: The sample size was small. CONCLUSIONS: This study showed that intracorporeal attachable and detachable instruments were safe and feasible for this procedure.


Assuntos
Colectomia/instrumentação , Colectomia/métodos , Neoplasias do Colo/cirurgia , Laparoscopia/métodos , Idoso , Idoso de 80 Anos ou mais , Perda Sanguínea Cirúrgica , Estudos de Viabilidade , Feminino , Humanos , Tempo de Internação , Masculino , Pessoa de Meia-Idade , Complicações Pós-Operatórias , Estudos Prospectivos , Instrumentos Cirúrgicos , Resultado do Tratamento
17.
J Mol Biol ; 348(1): 195-204, 2005 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-15808863

RESUMO

We report the effects of allosteric effectors, ATP, CTP and UTP on the kinetics of the quaternary structure change of Escherichia coli ATCase during the enzyme reaction with physiological substrates. Time-resolved, small-angle, X-ray scattering of solutions allows direct observation of structural transitions over the entire time-course of the enzyme reaction initiated by fast mixing of the enzyme and substrates. In the absence of effectors, all scattering patterns recorded during the reaction are consistent with a two-state, concerted transition model, involving no detectable intermediate conformation that differs from the less active, unliganded T-state and the more active, substrate-bound R-state. The latter predominates during the steady-state phase of enzyme catalysis, while the initial T-state is recovered after substrate consumption. The concerted character of the structural transition is preserved in the presence of all effectors. CTP slightly shifts the dynamical equilibrium during a shortened steady state toward T while the additional presence of UTP makes the steady state vanishingly short. The return transition to the T conformation is slowed significantly in the presence of inhibitors, the effect being most severe in the presence of UTP. While ATP increases the apparent T to R rate, it also increases the duration of the steady-state phase, an apparently paradoxical observation. This observation can be accounted for by the greater increase in the association rate constant of aspartate, promoted by ATP, while the nucleotide produces a lesser degree of increase in the dissociation rate constant. Under our experimental conditions, using high concentrations of both enzyme and substrate, it appears that this very mechanism of activation turns the activator into an efficient inhibitor. The scattering patterns recorded in the presence of ATP support the view that ATP alters the quaternary structure of the substrate-bound enzyme, an effect reminiscent of the reported modification of PALA-bound R-state by Mg-ATP.


Assuntos
Aspartato Carbamoiltransferase/química , Nucleotídeos/metabolismo , Estrutura Quaternária de Proteína , Regulação Alostérica , Aspartato Carbamoiltransferase/metabolismo
18.
J Biosci Bioeng ; 98(2): 67-70, 2004.
Artigo em Inglês | MEDLINE | ID: mdl-16233668

RESUMO

A novel 55-kDa hydroxylase was isolated from cultured cells of Catharanthus roseus by a three-step procedure: anion exchange chromatography, affinity chromatography and hydroxylapatite adsorption chromatography. The enzyme specifically catalyzed the hydroxylation of 2-hydroxybenzoic acid to give 2,5-dihydroxybenzoic acid. The enzyme activity was optimal at pH 7.8 and was completely inhibited by divalent cations, such as Cu(2+) and Hg(2+). The enzyme showed sequence similarity to certain plant flavonoid 3'-hydroxylases.

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