title: Enzymatic changes of the bovine pituitary multicatalytic proteinase complex, induced by magnesium ions.
abstract: The effect of magnesium ions on the catalytic activities of the bovine pituitary multicatalytic proteinase complex (MPC) was studied. Mg2+ markedly stimulated the breakdown of dephosphorylated beta-casein (caseinolytic activity) and the hydrolysis of Cbz-Leu-Leu-Glu-2-naphthylamide (peptidylglutamyl peptide bond hydrolyzing activity) by a 1700-fold purified preparation of MPC. Cleavage of Cbz-D-Ala-Leu-Arg-2-naphthylamide (trypsin-like activity) was strongly inhibited and cleavage of Cbz-Gly-Gly-Leu-p-nitroanilide (chymotrypsin-like activity) was weakly inhibited. Similar results were produced when enzymatic activities in the absence of Mg2+ were measured at 52 degrees C rather than at 37 degrees C. Trace protein impurities were removed by phenyl-Sepharose chromatography. This additional chromatographic step, while not changing the specific activities of hydrolysis of the three synthetic chromogenic substrates, led to a marked activation of the breakdown of dephosphorylated beta-casein. Mg2+ was not able to further stimulate the caseinolytic activities of either the phenyl-Sepharose-treated preparation or the preparation measured at 52 degrees C. Mg2+ therefore converts a "repressed" form of MPC to an "activated" form, possibly by promoting dissociation of a protein inhibitor, and may serve as a physiological regulator of this enzyme complex.
authors.affiliation: Mount Sinai School of Medicine, City University of New York, New York 10029.
authors.forename: M E
authors.initials: ME
authors.lastname: Pereira
authors.forename: B
authors.initials: B
authors.lastname: Yu
authors.forename: S
authors.initials: S
authors.lastname: Wilk
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000378:metabolism; D002417:Cattle; D002846:Chromatography, Affinity; D002863:Chromogenic Compounds / Q000378:metabolism; D002918:Chymotrypsin / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D010902:Pituitary Gland / Q000201:enzymology*; D046988:Proteasome Endopeptidase Complex; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism
chemical_list: D002364:Caseins; D002863:Chromogenic Compounds; D009097:Multienzyme Complexes; D009842:Oligopeptides; D010446:Peptide Fragments; D012967:Sodium Dodecyl Sulfate; D002918:Chymotrypsin; D014357:Trypsin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008274:Magnesium