Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P30536 (PBS)
 9,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A recognition site for benzodiazepines structurally different from that linked to various gamma-aminobutyric acid A (GABAA) receptor subtypes is located on the outer mitochondrial membranes of steroidogenic cells. This protein has been signified to be important in the regulation of steroid biosynthesis. Because of its location it is designated herein as the mitochondrial benzodiazepine receptor (MBR). A putative endogenous ligand for MBR is the peptide diazepam binding inhibitor (DBI), previously shown to displace drugs from MBR and to be expressed and stored in steroidogenic cells rich in MBR. The two model systems used to study steroidogenic regulation by DBI were the Y-1 adrenocortical and MA-10 Leydig cell lines previously shown to be applicable in studies of mitochondrial steroidogenesis. Both cell lines contain DBI as well as DBI processing products, including the DBI fragments that on reverse phase HPLC coelute with the naturally occurring triakontatetraneuropeptide [TTN; DBI-(17-50)] and octadecaneuropeptide [DBI-(33-50)]. When DBI purified from rat brain was added to mitochondria prepared from Y-1 and MA-10 cell lines, it increased the rates of pregnenolone formation in a dose-related manner. In both cell lines, maximal stimulation (3-fold) of mitochondrial steroidogenesis was obtained with 0.33 microM DBI, with an EC50 of approximately 0.1 microM. However, DBI concentrations higher than 1 microM caused a smaller increase in pregnenolone formation. Flunitrazepam, a benzodiazepine that binds with high nanomolar affinity to MBR, was recently shown to act as an antagonist of ACTH and LH/hCG-induced steroidogenesis and was found in the present studies to inhibit DBI-stimulated mitochondrial steroidogenesis. During the incubation with mitochondria, DBI was partially processed to different peptide fragments, including octadecaneuropeptide and TTN. To determine whether DBI processing products influence mitochondrial steroid biosynthesis, several DBI fragments and other peptides structurally unrelated to DBI were tested. Among these, only TTN stimulated mitochondrial steroid synthesis in a dose-dependent manner similar to DBI.
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PMID:Diazepam binding inhibitor and its processing products stimulate mitochondrial steroid biosynthesis via an interaction with mitochondrial benzodiazepine receptors. 165 52

The rate-limiting step in the biosynthesis of steroids is the transport of the substrate cholesterol from the outer to the inner mitochondrial membrane, where cholesterol is metabolized to pregnenolone. This transport is markedly stimulated by the action of hormones, such as adrenocorticotropic hormone (ACTH) and luteinizing hormone (LH) for adrenocortical and testicular Leydig cells, respectively. Recently, it was demonstrated that the peripheral-type or mitochondrial benzodiazepine receptor, abundant in steroidogenic tissues, is involved in the regulation of steroid biosynthesis. In search for an endogenous ligand for mitochondrial benzodiazepine receptors, regulating steroidogenesis, the effects of Diazepam Binding Inhibitor (DBI) were studied. The model systems used were the Y-1 adrenocortical and the MA-10 Leydig cell lines, previously shown to be valid steroidogenic models. Both cell lines contain significant levels of immunoreactive DBI. Purified DBI from rat brain, at high nanomolar concentrations, increased formation of pregnenolone, when added to mitochondrial preparations of both cell types; but at concentrations of DBI above 1 microM, a decrease in the stimulation was observed. Flunitrazepam, a benzodiazepine which binds to mitochondrial benzodiazepine receptors, with high nanomolar affinity, inhibited the stimulatory action of DBI on the formation of mitochondrial pregnenolone, indicating that DBI exerts its stimulatory effects through an action on mitochondrial benzodiazepine receptors. In order to determine the biologically active amino acid sequence in the DBI molecule, various fragments of DBI were synthesized and tested; also, peptides structurally unrelated to DBI were tested.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The role of diazepam binding inhibitor and its processing products at mitochondrial benzodiazepine receptors: regulation of steroid biosynthesis. 166 68