ENZYMATIC CHANGES OF THE BOVINE PITUITARY MULTICATALYTIC PROTEINASE COMPLEX, INDUCED BY MAGNESIUM-IONS

被引:45
作者
PEREIRA, ME [1 ]
YU, B [1 ]
WILK, S [1 ]
机构
[1] CUNY MT SINAI SCH MED,DEPT PHARMACOL,NEW YORK,NY 10029
关键词
D O I
10.1016/0003-9861(92)90128-J
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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 β-casein (caseinolytic activity) and the hydrolysis of CbzLeuLeuGlu-2-naphthylamide (peptidylglutamyl peptide bond hydrolyzing activity) by a 1700-fold purified preparation of MPC. Cleavage of CbzD-AlaLeuArg-2-naphthylamide (trypsin-like activity) was strongly inhibited and cleavage of CbzGlyGlyLeup-nitroanilide (chymotrypsin-like activity) was weakly inhibited. Similar results were produced when enzymatic activities in the absence of Mg2+ were measured at 52 °C rather than at 37 °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 β-casein. Mg2+ was not able to further stimulate the caseinolytic activities of either the phenyl-Sepharose-treated preparation or the preparation measured at 52 °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. © 1992.
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页码:1 / 8
页数:8
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