Protein methylases I, II and III were detected in extracts of , and characterized according to the specific amino substituent methylated. Only protein methylase II activity was elevated by difluoromethylornithine treatment of , and hence this enzyme was characterized further. Protein methylase II transferred methyl groups from -adenosyl-l-methionine (-AdoMet) to the carboxyl residues of several protein substrates, exhibiting highest activity with histone VIII-S (arginine-rich subgroup f). The crude enzyme had an apparent for histone VIII-S of 28 mg ml (11.4 mM-aspartyl and 18.4 mM-glutamyl residues methylated), and an apparent for -AdoMet of 8.4 μM. protein methylase II was sensitive to inhibition by -adenosyl-l-homocysteine and its analogue sinefungin with apparent values of 12.9 and 1.6 μm, respectively. Using a partially purified preparation, analysis of kinetic data in the presence and absence of sinefungin indicated that this analogue acts as a competitive inhibitor of the -AdoMet binding site, and as a non-competitive inhibitor of the (protein) histone VIII-S binding site. The possible role of the enzyme in morphological control and its potential as a chemotherapeutic target are discussed.


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