Activation of the multicatalytic proteinase from rat skeletal muscle by fatty acids or sodium dodecyl sulphate

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Abstract
A multicatalytic proteinase from rat skeletal muscle contains active site(s) catalyzing the degradation of benzoyl-Val-Gly-Arg 4-methyl-7-coumarylamide, succinyl-Ala-Ala-Phe 4-methylcoumarylamide and [14C]methylcasein, as well as benzyloxycarbonyl-Leu-Leu-Glu 2-naphthylamide. These activities are 7- to 14-fold activated by 1 mM-sodium dodecyl sulfate [SDS]. The activation leads to a higher susceptibility to the proteinase inhibitor chymostatin and to a lower ability to be inhibited and precipitated by antibodies raised against the non-activated enzyme. Since no changes in MW or subunit composition were observed in the SDS-activated form, some conformational changes seem to occur during the activation step. More pronounced activation was observed in the presence of physiological concentrations of fatty acids; oleic acid at 100 .mu.M concentrations stimulated the proteinase .apprx. 50-fold. In contrast with the non-activated proteinase, the activated enzyme considerably degrades muscle cytoplasmic proteins in vitro. Thus it is not unlikely that, in vivo, potential activators such as fatty acids can induce the multicatalytic proteinase to participate in muscle protein breakdown.