A protein kinase (EC 2.7.1.37) which phosphorylates histones was purified partially from the soluble fractions of cultured plant cells. The optimum pH was 7.5 to 9.0. The activity wasnot stimulated by exogeneous cyclic AMP. It was thermolabile and completely dependent on the presence of Mg2+ or Mn2+ for activity. p-Chloromercuribenzoate inactivated this enzyme and this inactivation was overcome by mercaptoethanol.
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