Enzymatic changes of the bovine pituitary multicatalytic proteinase complex, induced by magnesium ions

Arch Biochem Biophys. 1992 Apr;294(1):1-8. doi: 10.1016/0003-9861(92)90128-j.


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.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Caseins / metabolism
  • Cattle
  • Chromatography, Affinity
  • Chromogenic Compounds / metabolism
  • Chymotrypsin / metabolism
  • Cysteine Endopeptidases / metabolism*
  • Magnesium / pharmacology*
  • Molecular Sequence Data
  • Multienzyme Complexes / metabolism*
  • Oligopeptides / metabolism
  • Peptide Fragments / metabolism
  • Pituitary Gland / enzymology*
  • Proteasome Endopeptidase Complex
  • Sodium Dodecyl Sulfate / pharmacology
  • Substrate Specificity
  • Trypsin / metabolism


  • Caseins
  • Chromogenic Compounds
  • Multienzyme Complexes
  • Oligopeptides
  • Peptide Fragments
  • Sodium Dodecyl Sulfate
  • Chymotrypsin
  • Trypsin
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Magnesium