title: Isolation of a precursor and a nascent chain form of glucose-6-phosphate dehydrogenase from rat uterus and regulation of precursor processing by estradiol.
abstract: SDS-polyacrylamide gel electrophoresis of anti-glucose-6-phosphate dehydrogenase immunoprecipitates from radiolabeled uterine tissue extracts previously revealed three proteins: A, B and C, which were tentatively identified as a 60-64 kDa precursor form, a 57 kDa predominant form, and a 40-42 kDa nascent peptide form of the enzyme, respectively. A peptide-mapping technique was used to examine structural homologies among A, B and C. Following the labeling of uterine proteins with [35S]methionine, labeled proteins A, B and C were isolated by immunoprecipitation and electrophoresis. Each protein was individually co-digested with authentic, [3H]methionine-labeled glucose-6-phosphate dehydrogenase using papain, the resulting peptides were resolved by isoelectric focusing and the peptides from the two sources on each gel were compared using double-label counting methods. Proteins A, B and C had at least eight peptides in common, both proteins A and C had two additional peptides in common that were not present in protein B, and B protein had two peptides that were either absent or present in reduced amounts in digests of proteins A and C. The extensive structural homology and immunoreactivity of these proteins indicated that proteins A, B and C were all related to glucose-6-phosphate dehydrogenase. The presence of two extra peptides in proteins A and C suggested that these peptides may be derived from a common NH2-terminal leader sequence which was present in both the precursor and nascent peptide chains. The presence of two peptides that were present in protein B and absent from proteins A and C is easiest to explain if they are derived from the two ends of the molecule, with the corresponding peptides in proteins A and C containing additional peptide sequences that are 'normally' removed by endogenous proteolytic processing enzymes. Based on the relative time-course of synthesis of the three glucose-6-phosphate dehydrogenase-related proteins in control and estrogen-treated uteri, it appears that estradiol promotes an increase in the relative rate of transfer of label from protein A into B by stimulating the rate of processing of the precursor to the predominant form of the enzyme and enhances the rate of translational conversion of protein C into higher molecular weight forms.
mesh_terms: D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000302:isolation & purification*; D004958:Estradiol / Q000502:physiology*; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000096:biosynthesis / Q000302:isolation & purification*; D007120:Immunochemistry; D007202:Indicators and Reagents; D007525:Isoelectric Focusing; D008715:Methionine / Q000032:analysis; D010206:Papain; D010446:Peptide Fragments / Q000032:analysis; D011499:Protein Processing, Post-Translational; D051381:Rats; D014599:Uterus / Q000201:enzymology*
chemical_list: D004792:Enzyme Precursors; D007202:Indicators and Reagents; D010446:Peptide Fragments; D004958:Estradiol; D008715:Methionine; D005954:Glucosephosphate Dehydrogenase; D010206:Papain