MAMMALIAN MICROSOMAL AND SOLUBLE RAS-PROCESSING PEPTIDASE ACTIVITIES ARE DISTINCT

Microsomal and soluble peptidases from bovine liver and pig brain hydr olyze the farnesylated, Ras-based CAAX peptide [H-3]Ac-fCVIM-OH. Howev er, they differ in their sensitivity to substrate-based inhibitors, su lfhydryl and chelating agents, pH and ionic strength optima, and stabi lity. The microsomal activity was exquisitely sensitive to the substra te-based inhibitor Boc-fC[CH2]VIM-ON, moderately sensitive to the sulf hydryl agent pCMB, but insensitive to NEM and the metal-chelating agen t o-phenanthroline. The soluble activity was insensitive to Boc-fC[CH2 ]VIM-OH, but very sensitive to pCMB, NEM and o-phenanthroline, suggest ing it to be the previously reported (Biochem. Biophys. Res. Commun. 1 98, 787-794 (1994)) zinc metallopeptidase. The microsomal activity is most likely to be a cysteine peptidase involved in the posttranslation al processing of Ras proteins.