[A case of HIV combined with Mycobacterium celatum infection].

Here, we reported the diagnosis and treatment of a case of HIV infected person complicated by an extremely rare infection with Mycobacterium celatum. Due to the similarity of homologous sequence regions between Mycobacterium celatum and Mycobacterium tuberculosis complex, the identification of conventional Mycobacterium species was incorrect, which was corrected after first-generation 16S rRNA sequencing. This report aimed to improve the clinical understanding of Mycobacterium celatum infection and the level of differential diagnosis between non-tuberculous mycobacterial disease and tuberculosis.

[Ruxolitinib combined with liposomal doxorubicin, etoposide, methylprednisolone+/-PEG-asparaginase in treatment of relapsed/refractory pediatric hemophagocytic lymphohistiocytosis].

Objective: To investigate the efficacy and safety of ruxolitinib, liposomal doxorubicin, etoposide, methylprednisolone+/-PEG-asparaginase (RU-DEP+/-L) in the treatment of relapsed/refractory (R/R) pediatric hemophagocytic lymphohistiocytosis (HLH). Methods: The clinical data of R/R pediatric HLH, who accepted the RU-DEP+/-L regimen at Beijing Children's Hospital from January 2018 to December 2019 was retrospectively analyzed. Results: A total of 16 patients were included in this study, including 13 males and 3 females, aged[M(Q1,Q3)] 1 (1, 2) years at diagnosis. Thirteen patients were diagnosed with Epstein-Barr virus (EBV)-HLH, 2 with EBV-induced primary HLH, and 1 with unclear etiology, among which 3 patients were co-infected with CMV. After the first-line treatment, 11 patients had no response, and 5 patients relapsed after complete response. Nine patients received the RU-L-DEP regimen, and 7 patients received the RU-DEP regimen. The overall response rate and complete response of RU-DEP+/-L treatment were 10/16 and 3/16, respectively. The negative conversion rate of plasma EBV-DNA was 7/15. The median follow-up time was 35.1 (2.4, 40.7) months, and 9/16 patients were survival. The 3-year overall survival rate after RU-DEP+/-L treatment in response and accepted hematopoietic stem cell transplantation (HSCT) was higher than that without response and did not receive HSCT (P=0.048). Among the 16 patients, 9 had varying degrees of myelosuppression, and 13 had an infection. Conclusions: RU-DEP+/-L can be used as a salvage treatment in R/R pediatric HLH, which can provide a bridge to HSCT and play an important role in the control of HLH. The main adverse reactions are myelosuppression and infection, which can be tolerated.

A scalable method to concentrate lentiviral vectors pseudotyped with measles virus glycoproteins.

Lentiviral (LV) vectors have emerged as powerful tools for basic research and clinical applications because of their ability to stably transduce both dividing and nondividing cells. A wide range of viral envelope (Env) glycoproteins have the ability to associate with the membrane of LV vectors, a process that is referred to as pseudotyping. Pseudotyped vectors have the capacity to transduce specific cell types for specific applications. For example, LV vectors pseudotyped with the measles virus (MV)-derived hemagglutinin (H) and fusion (F) proteins have the ability to transduce quiescent lymphocytes. In addition, the MV H glycoprotein can be engineered allowing cell-specific targeting of LV vectors. One problem with MV glycoprotein-pseudotyped LV vectors is low titer during vector production. This results in the need to manufacture large volumes of the vectors and to concentrate them to appropriate titers. The commonly used centrifugation-based concentration techniques for LV vectors are not practical for large-scale vector manufacturing. Thus, there is a need for improved methods to concentrate LV vectors. In this study, we adapted an anion-exchange membrane chromatography method that we previously used in the context of LV vectors pseudotyped with the vesicular stomatitis virus glycoprotein to concentate MV glycoprotein-pseudotyped LV vectors. Up to 60% of the input vectors with an up to 5300-fold reduction in volume was achieved using this anion-exchange chromatography method in conjunction with a desalting/concentration step involving centrifugal filter units. This technique provides a rapid and scalable approach for concentrating MV-pseudotyped LV vectors that does not require an elaborate setup.

Randomized phase III trial of prophylactic cranial irradiation versus observation in patients with fully resected stage IIIA-N2 nonsmall-cell lung cancer and high risk of cerebral metastases after adjuvant chemotherapy.

BACKGROUND: This study compared prophylactic cranial irradiation (PCI) with observation in patients with resected stage IIIA-N2 non-small-cell lung cancer (NSCLC) and high risk of cerebral metastases after adjuvant chemotherapy. PATIENTS AND METHODS: In this open-label, randomized, phase III trial, patients with fully resected postoperative pathologically confirmed stage IIIA-N2 NSCLC and high cerebral metastases risk without recurrence after postoperative adjuvant chemotherapy were randomly assigned to receive PCI (30 Gy in 10 fractions) or observation. The primary end point was disease-free survival (DFS). The secondary end points included the incidence of brain metastases, overall survival (OS), toxicity and quality of life. RESULTS: This trial was terminated early after the random assignment of 156 patients (81 to PCI group and 75 to control group). The PCI group had significantly lengthened DFS compared with the control group, with a median DFS of 28.5 months versus 21.2 months [hazard ratio (HR), 0.67; 95% confidence interval (CI) 0.46-0.98; P = 0.037]. PCI was associated with a decrease in risk of brain metastases (the actuarial 5-year brain metastases rate, 20.3% versus 49.9%; HR, 0.28; 95% CI 0.14-0.57; P < 0.001). The median OS was 31.2 months in the PCI group and 27.4 months in the control group (HR, 0.81; 95% CI 0.56-1.16; P = 0.310). While main toxicities were headache, nausea/vomiting and fatigue in the PCI group, they were generally mild. CONCLUSION: In patients with fully resected postoperative pathologically confirmed stage IIIA-N2 NSCLC and high risk of cerebral metastases after adjuvant chemotherapy, PCI prolongs DFS and decreases the incidence of brain metastases.

Multipoint targeting of the PI3K/mTOR pathway in mesothelioma.

BACKGROUND: Mesothelioma is a notoriously chemotherapy-resistant neoplasm, as is evident in the dismal overall survival for patients with those of asbestos-associated disease. We previously demonstrated co-activation of multiple receptor tyrosine kinases (RTKs), including epidermal growth factor receptor (EGFR), MET, and AXL in mesothelioma cell lines, suggesting that these kinases could serve as novel therapeutic targets. Although clinical trials have not shown activity for EGFR inhibitors in mesothelioma, concurrent inhibition of various activated RTKs has pro-apoptotic and anti-proliferative effects in mesothelioma cell lines. Thus, we hypothesised that a coordinated network of multi-RTK activation contributes to mesothelioma tumorigenesis. METHODS: Activation of PI3K/AKT/mTOR, Raf/MAPK, and co-activation of RTKs were evaluated in mesotheliomas. Effects of RTK and downstream inhibitors/shRNAs were assessed by measuring mesothelioma cell viability/growth, apoptosis, activation of signalling intermediates, expression of cell-cycle checkpoints, and cell-cycle alterations. RESULTS: We demonstrate activation of the PI3K/AKT/p70S6K and RAF/MEK/MAPK pathways in mesothelioma, but not in non-neoplastic mesothelial cells. The AKT activation, but not MAPK activation, was dependent on coordinated activation of RTKs EGFR, MET, and AXL. In addition, PI3K/AKT/mTOR pathway inhibition recapitulated the anti-proliferative effects of concurrent inhibition of EGFR, MET, and AXL. Dual targeting of PI3K/mTOR by BEZ235 or a combination of RAD001 and AKT knockdown had a greater effect on mesothelioma proliferation and viability than inhibition of individual activated RTKs or downstream signalling intermediates. Inhibition of PI3K/AKT was also associated with MDM2-p53 cell-cycle regulation. CONCLUSIONS: These findings show that PI3K/AKT/mTOR is a crucial survival pathway downstream of multiple activated RTKs in mesothelioma, underscoring that PI3K/mTOR is a compelling target for therapeutic intervention.

Rapid titration of retroviral vectors using a ß-lactamase protein fragment complementation assay.

The availability of rapid and quantitative titration assays for retroviral vectors is important, especially in the context of clinical applications. In this report, we describe a novel assay to titrate lentiviral and gamma retroviral vectors. This rapid assay is based on protein fragment complementation involving the N-terminal (Bla1) and the C-terminal (Bla2) fragments of TEM-1 ß-lactamase (BLAK). The Bla1 protein fragment is incorporated in the vector's envelope during vector production. Bla1-bearing vectors are titrated on Bla2-expressing cells. Upon transduction, Bla1 and Bla2 heterodimerize and restore BLAK's enzymatic function. The enzymatic activity of BLAK is quantified by flow cytometry using the green fluorescent CCF2/AM substrate, which is converted into a blue fluorescent product. The enzymatic conversion of the CCF2/AM substrate was found to be directly related to vector entry, as a neutralizing antibody completely blocked the conversion. The titers obtained using this rapid assay correlated well with the titers measured by functional transduction assays. The whole assay can be finished within 8 h. Thus, it is considerably less time consuming compared with other transduction-based titration assays for lentiviral and gamma retroviral vectors.

RKIp inhibits the migration and invasion of human prostate cancer PC-3M cells through regulation of extracellular matrix.

Raf kinase inhibitor protein (RKIP) plays a pivotal role in several intracellular signaling cascades and has been implicated as a metastasis suppressor in multiple cancer cells including prostate cancer cells, but the mechanism is not very clear. In this study, we investigated the effect of RKIP on cell proliferation, migration and invasion using human prostate cancer PC-3M cells as a model system. Our results indicate that RKIP does not effect cell proliferation in PC-3M cells, but inhibits both cell migration and cell invasion. In association with this inhibitory effect, RKIP down-regulates matrix metalloproteinases (MMP-2 and MMP-9), cathepsin B and urinary plasminogen activator (uPA). Also RKIP has the ability to regulate the expression of E-cadherin. But ectopic expression of RKIP does not affect the level of the Snail protein. As it has been indicated here, RKIP inhibits the migration and invasion ability of human prostate cancer cells through regulation of the extracellular matrix. These findings provide new mechanistic insight how RKIP suppresses metastasis in vitro.

[Prediction of perioperative hyperkalemia in dialysis patients with secondary hyperparathyroidism].

Objective: To explore the influencing factors for serum potassium >4.4 mmol/L in the morning of parathyroidectomy in hemodialysis patients with secondary hyperparathyroidism (SHPT). Methods: The clinical data of 72 patients with SHPT who received regular hemodialysis and underwent parathyroidectomy in Guangdong Provincial People's Hospital from January 2012 to December 2018 were analyzed retrospectively. There were 37 males and 35 females, aged from 25 to 69 years, and the dialysis timespan was from 0.5 to 11 years. The levels of parathyroid hormone, serum potassium and serum calcium before hemodialysis were examined one day before operation, and hemodialysis time and dewatering volume after hemodialysis without heparin were recorded, and also the level of serum potassium in the morning of parathyroidectomy was detected. The occurrences of hyperkalemia during and after operation were studied. The factors related to hyperkalemia in the morning of parathyroidectomy were evaluated by Pearson or Spearman correlation analysis, and the cut-off values of risk factors were calculated by receiver operating characteristic (ROC) curve. Results: Serum potassium >4.4 mmol/L in the morning of parathyroidectomy existed in 23 of 72 patients. Correlation analysis showed that serum potassium one day before operation ((4.93±0.56)mmol/L, r=0.656, P<0.001) and dehydration volume ((2.37±0.75)L, r=0.261, P=0.027) were positively correlated with serum potassium in the morning of parathyroidectomy((4.16±0.54)mmol/L). Serum potassium before hemodialysis one day before operation was a main predictor for serum potassium in the morning of parathyroidectomy (AUC=0.791, P<0.001). The cut-off value of serum potassium before hemodialysis one day before operation was 5.0 mmol/L. Conclusion: Serum potassium before hemodialysis one day before operation in patients with SHPT can predict serum potassium in the morning of parathyroidectomy, offering imformation for the safety of operation.

Serial femtosecond and serial synchrotron crystallography can yield data of equivalent quality: A systematic comparison.

For the two proteins myoglobin and fluoroacetate dehalogenase, we present a systematic comparison of crystallographic diffraction data collected by serial femtosecond (SFX) and serial synchrotron crystallography (SSX). To maximize comparability, we used the same batch of micron-sized crystals, the same sample delivery device, and the same data analysis software. Overall figures of merit indicate that the data of both radiation sources are of equivalent quality. For both proteins, reasonable data statistics can be obtained with approximately 5000 room-temperature diffraction images irrespective of the radiation source. The direct comparability of SSX and SFX data indicates that the quality of diffraction data obtained from these samples is linked to the properties of the crystals rather than to the radiation source. Therefore, for other systems with similar properties, time-resolved experiments can be conducted at the radiation source that best matches the desired time resolution.

Efficient gene transfer using the human JC virus-like particle that inhibits human colon adenocarcinoma growth in a nude mouse model.

The JC virus (JCV) may infect human oligodendrocytes and consequently cause progressive multifocal leukoencephalopathy (PML) in patients with immune deficiency. In addition, the virus has also been detected in other human tissues, including kidney, B lymphocytes, and gastrointestinal tissue. The recombinant major structural protein, VP1, of JCV is able to self-assemble to form a virus-like particle (VLP). It has been shown that the VLP is capable of packaging and delivering exogenous DNA into human cells for gene expression. However, gene transfer is not efficient when using in vitro DNA packaging methods with VLPs. In this study, a novel in vivo DNA packaging method using the JCV VLP was used to obtain high efficiency gene transfer. A reporter gene, the green fluorescence protein, and a suicide gene, the herpes simplex virus thymidine kinase (tk), were encapsidated into VLPs in Escherichia coli. The VLP was used to specifically target human colon carcinoma (COLO-320 HSR) cells in a nude mouse model. Intraperitoneal administration of ganciclovir in the tk-VLP-treated mice greatly reduced tumor volume. These findings suggest that it will be possible to develop the JCV VLP as a gene delivery vector for human colon cancer therapy in the future.

Asymptomatic COVID-19 infection in patients with cancer at a cancer-specialized hospital in Wuhan, China - Preliminary results.

OBJECTIVE: Patients with cancer are usually immunosuppressive and susceptible to COVID-19 infection. Asymptomatic COVID-19 cases are infective and cannot be identified by symptom-based screening. There is an urgent need to control virus spread by asymptomatic carriers at cancer centres. We aim to describe the characteristics, screening methods, and outcomes of cancer patients with asymptomatic COVID-19 infection and to further explore anti-tumour treatment for this population. PATIENTS AND METHODS: We reviewed patients with cancer who were admitted to Hubei Cancer Hospital in Wuhan from February 1, 2020, to April 4, 2020. We collected demographic data, laboratory findings, treatment information, nucleic acid and serum test results, chest computed tomography (CT) information and survival status of cancer patients diagnosed with asymptomatic COVID-19 infection. RESULTS: A total of 16 cancer patients with asymptomatic COVID-19 infection were confirmed. The most common cancer type was breast cancer. The blood cell counts of most patients were in the normal range. Lymphocytes of 100% of asymptomatic carriers were in the normal range. Thirteen (81.3%) patients were positive for virus-specific IgM antibodies, and three (18.8%) were positive by PCR; only one (6.3%) patient showed novel coronavirus pneumonia features on CT. Three (18.3%) patients died, and the cause of death was considered malignancy caused by delaying anti-tumour treatment. CONCLUSIONS: Our study shows that the lymphocytes of 100% of asymptomatic carriers were in the normal range. This result indicates that the host immunity of asymptomatic carriers is not significantly disrupted by COVID-19. Single PCR detection is not sufficient to screen among asymptomatic individuals, and a combination of PCR tests, serological tests and CT is of great importance. Unless the tumour is life-threatening or rapidly progressing, we advise restarting active anti-tumour therapy after PCR tests become negative.

KIT oncoprotein interactions in gastrointestinal stromal tumors: therapeutic relevance.

Most gastrointestinal stromal tumors (GISTs) express oncogenic and constitutively active forms of the KIT or platelet-derived growth factor receptor alpha (PDGFRA) receptor tyrosine kinase proteins, and these kinase oncoproteins serve as targets for effective therapies. Given that mutant KIT oncoproteins serve crucial transforming roles in GISTs, we evaluated interactions with the KIT oncoproteins and determined signaling pathways that are dependent on KIT oncogenic activation in GISTs. Tyrosine-phosphorylated KIT oncoproteins interacted with PDGFRA, PDGFRB, phosphatidylinositol 3-kinase (PI3-K) and PKCtheta in GIST cells, and these interactions were abolished by KIT inhibition with imatinib or PKC412 or KIT RNAi. Notably, tyrosine-phosphorylated PDGFRA was prominent in frozen GIST tumors expressing KIT oncoproteins, suggesting that KIT-mediated PDGFRA phosphorylation is an efficient and biologically consequential mechanism in GISTs. Activated signaling intermediates were identified by immunoaffinity purification of tyrosine-phosphorylated proteins in GIST cells before and after treatment with KIT inhibitors, and these analyses show that GRB2, SHC, CBL and MAPK activation are largely KIT dependent in GISTs, whereas PI3-K, STAT1 and STAT3 activation are partially KIT dependent. In addition, we found that phosphorylation of several tyrosine kinase proteins - including JAK1 and EPHA4 - did not depend on KIT activation. Likewise, paxillin activation was independent of the KIT oncogenic signal. These studies identify signaling pathways that can provide both KIT-dependent and KIT-independent therapeutic synergies in GIST, and thereby highlight clinical strategies that might consolidate GIST therapeutic response to KIT/PDGFRA inhibition.

Metabolic Biomarkers of Aging and Aging-related Diseases in Chinese Middle-Aged and Elderly Men.

BACKGROUND: Aging is an acknowledged risk factor for most chronic diseases and functional impairments. The practicability of potential biomarkers of aging remains unsure. Moreover, biomarkers related to certain geriatric diseases, such as carotid atherosclerosis and multiple co-morbidities are less understood. The purpose of this study was to investigate the definite relationship between metabolic biomarkers and aging-related diseases. METHODS: Eighty-five male adults aged fifty years or older from the general population were enrolled. Plasma metabolic biomarkers, including fourteen amino acids and thirty-six acylcarnitines, were measured by liquid chromatography mass spectrometry. Bivariate correlation analysis was employed to estimate the correlations between variables and age, and also to evaluate the relationship between metabolic biomarkers and aging-related diseases. Receiver operating characteristic (ROC) curve was conducted to judge the diagnostic efficiency of potential metabolic biomarkers for co-morbidities. RESULTS: Certain metabolic biomarkers were strongly positively correlated with age, such as tetradecenoylcarnitine (C14:1), microalbumin-urine creatinine ratio (UACR), dodecenoylcarnitine (C12:1) and citrulline (p < 0.001). Carotid atherosclerosis and co-morbidities were positively correlated with aging (p < 0.001). After adjustment for age, hydroxytetradecanoylcarnitine (C14OH) remained positively correlated with carotid plague area. Besides, citrulline had diagnostic power for co-morbidities. CONCLUSIONS: Citrulline may be a promising metabolic biomarker in the middle-aged and elderly men. Larger-scale and long-term studies are needed to confirm our findings.

Differential responses of antioxidative system to chilling and drought in four rice cultivars differing in sensitivity.

Responses of antioxidative defense systems to chilling and drought stresses were comparatively studied in four cultivars of rice (Oryza sativa L.) differing in sensitivity, two of them (Xiangnuo no. 1 and Zimanuo) are tolerant to chilling but sensitive to drought and the other two (Xiangzhongxian no. 2 and IR50) are tolerant to drought but sensitive to chilling. The seedlings of rice were transferred into growth chamber for 5 d at 8 degrees C as chilling treatment, or at 28 degrees C as control, or at 28 degrees C but cultured in 23% PEG-6000 solution as drought stress treatment. Under drought stress the elevated levels of electrolyte leakage, contents of H(2)O(2) and total thiobarbituric acid-reacting substances (TBARS) in Xiangzhongxian no. 2 and IR50 are lower than those in Xiangnuo no. 1 and Zimanuo. On the contrary, Xiangnuo no. 1 and Zimanuo have much lower level of electrolyte leakage, H(2)O(2) and TBARS than Xiangzhongxian no. 2 and IR50 under chilling stress. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase, and ascorbate-peroxidase (APX)) and contents of antioxidants (ascorbaic acid and reduced glutathione) were measured during the stress treatments. All of them were enhanced greatly until 3 d after drought stress in the two drought-tolerant cultivars, or after chilling stress in the two chilling-tolerant cultivars. They all were decreased at 5 d after stress treatments. On the other hand, activities of antioxidant enzymes and contents of antioxidants were decreased greatly in the drought-sensitive cultivars after drought stress, or in the chilling-sensitive cultivars after chilling stress. The results indicated that tolerance to drought or chilling in rice is well associated with the enhanced capacity of antioxidative system under drought or chilling condition, and that the sensitivity of rice to drought or chilling is linear correlated to the decreased capacity of antioxidative system.

Chaperone-like activity of peptidyl-prolyl cis-trans isomerase during creatine kinase refolding.

Porcine kidney 18 kD peptidyl-prolyl cis-trans isomerase (PPIase) belongs to the cyclophilin family that is inhibited by the immunosuppressive drug cyclosporin A. The chaperone activity of PPIase was studied using inactive, active, and alkylated PPIase during rabbit muscle creatine kinase (CK) refolding. The results showed that low concentration inactive or active PPIase was able to improve the refolding yields, while high concentration PPIase decreased the CK reactivation yields. Aggregation was inhibited by inactive or active PPIase, and completely suppressed at 32 or 80 times the CK concentration (2.7 microM). However, alkylated PPIase was not able to prevent CK aggregation. In addition, the ability of inactive PPIase to affect CK reactivation and prevent CK aggregation was weaker than that of active PPIase. These results indicate that PPIase interacted with the early folding intermediates of CK, thus preventing their aggregation in a concentration-dependent manner. PPIase exhibited chaperone-like activity during CK refolding. The results also suggest that the isomerase activity of PPIase was independent of the chaperone activity, and that the proper molar ratio was important for the chaperone activity of PPIase. The cysteine residues of PPIase may be a peptide binding site, and may be an essential group for the chaperone function.

Disulfide bonds stabilize JC virus capsid-like structure by protecting calcium ions from chelation.

To investigate the role of disulfide bonds in the capsid structure, a recombinant JC virus-like particle (VLP) was used. The major capsid protein, VP1, of the JC virus was expressed in yeast cells. The yeast-expressed VP1 was self-assembled into a VLP. Disulfide bonds were found in the VLP which caused dimeric and trimeric VP1 linkages as demonstrated by non-reducing SDS-PAGE. The VLP remained intact when disulfide bonds were reduced by dithiothreitol. The VLP without disulfide bonds could be disassembled into capsomeres by EGTA alone, but those with disulfide bonds could not be disassembled by EGTA. Capsomeres were reassembled into VLPs in the presence of calcium ions. Capsomeres formed irregular aggregations instead of VLPs when treated with diamide to reconstitute the disulfide bonds. These results indicate that disulfide bonds play an important role in maintaining the integrity of the JC VLP by protecting calcium ions from chelation.

Specific binding of mitochondrial protein precursors to liposomes containing cardiolipin.

In vitro synthesized precursors of several mitochondrial proteins, including P-450(SCC), adrenodoxin, and malate dehydrogenase, bound to liposomes prepared from mitochondrial phospholipids, but not to those from microsomal phospholipids. When liposomes were prepared from various pure phospholipids, adrenodoxin precursor was bound only to the liposomes that contained cardiolipin. The liposomes containing other phospholipids did not show the binding affinity for the precursor. The binding was observed only with the precursor peptides of adrenodoxin and malate dehydrogenase, and their mature forms were not bound to the liposomes. The binding of the precursors was dependent on the concentration of cardiolipin in the liposomes. Liposomes containing various cardiolipin derivatives with modified polar head groups showed very different binding affinity for adrenodoxin precursor, suggesting the importance of the structure of the polar head of the cardiolipin molecule. Two or three positively charged amino acid residues in the extension peptide of P-450(SCC) precursor were replaced by neutral amino acid residues by site-directed mutagenesis. The mutated P-450(SCC) precursors did not bind to the liposomes containing cardiolipin. The results indicated that mitochondrial protein precursors have specific affinity for cardiolipin, and the affinity was due to the interaction between the extension peptides of the precursors and the polar head of the cardiolipin molecule.

Effects of synthetic model peptides resembling the extension peptides of mitochondrial enzyme precursors on import of the precursors into mitochondria.

One common and characteristic feature of the extension peptides of mitochondrial enzyme precursors is the presence of repeating short stretches of uncharged amino acids linked by basic amino acids. We synthesized several model peptides having this particular feature of the extension peptides. The peptides contained arginine or lysine as a basic amino acid residue linking sequences of two to four residues of leucine and alanine. We examined the effects of the peptides on the import of the precursors of two mitochondrial enzymes, cytochrome P-450(SCC) and adrenodoxin, and found that the peptides were generally inhibitory to the import of the precursors into mitochondria. The effective concentrations of some of the inhibitory peptides were as low as a few microM. The peptides containing lysine instead of arginine had an essentially similar inhibitory effect on the import. The peptides did not inhibit the binding of pre-P450(SCC) to the surface of mitochondria. The synthetic model peptides uncoupled oxidative phosphorylation of mitochondria prepared from either rat liver or bovine adrenal cortex, and induced leakage of enzymes from the inner compartments of mitochondria. However, the synthetic model peptides did not solubilize membrane-bound enzymes from mitochondria, suggesting that their effect on the membranes is different from that of detergents. The synthetic model peptides seem to bind to the membranes causing significant perturbation in the membrane structure, which is possibly related to the functions of the particular common sequence found in the extension peptides of mitochondrial enzyme precursors.