Action of mercurials on activity of partially purified soluble protein kinase C from mice brain.

The enzymatic activity of soluble protein kinase C from mice brain was inhibited by mercuric chloride (II) (HgCl2) and organic mercurials, i.e. methyl mercury, phenyl mercury and p-chloromercuribenzoic acid (PCMB). The IC50 was 0.08 microM for HgCl2 and about 1 microM for organic mercurials. Sulfhydryl blocking reagents such as 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) and N-ethylmaleimide (NEM) were less potent but nevertheless inhibited the enzymic activity of protein kinase C. The Hill coefficients of HgCl2, DTNB and NEM were close to unity whereas the values for organic mercurials were 1.3 to 1.5. The inhibition was of a non-competitive type with respect to H1 histone. 3H-PDBu binding activity was also inhibited by all of the reagents in a non-competitive manner. Mercurials apparently bind to sulfhydryl groups of protein kinase C to inhibit the enzymatic activity.