A Membrane-Bound Protease in Microsomes of Spinach Callus

Abstract

A di-isopropyl phosphorofluoridate-sensitive endopeptidase activity against some minor components of heat-denatured .alpha.-casein was detected in the endoplasmic reticulum and Golgi body-rich fraction of spinach callus. The activity was not solubilized with 0.05% sodium deoxycholate, but with 0.5% sodium cholate. The activity was strongly inhibited by deoxycholate (0.2-0.5%), di-isopropyl phosphorofluoridate, p-chloromercuric benzoate, o-phenanthroline, NiCl2, and ZnSO4, and moderately by phenylmethylsulfonyl fluoride, L-1-tosylamide-2-phenylethyl chloromethyl ketone, iodoacetic acid, EDTA, and FeSO4, and slightly by chymostatin. The inhibitory effect of o-phenanthroline was partially recovered with the addition of FeSO4 and ZnSO4.