REGULATION OF PROTEIN-PHOSPHORYLATION IN THE CYANOBACTERIUM ANABAENA STRAIN PCC-7120

Protein kinase activities have been detected in cell-free extracts of the cyanobacterium Anabaena PCC 7120. At least 12 polypeptides in the soluble fraction were phosphorylated in vitro at the expense of [gamma-32P]ATP and the pattern of phosphorylation was shown to be regulated by intermediary metabolites and other effectors, at physiological concentrations. Glucose 6-phosphate exerted a regulatory effect on a phosphopolypeptide of M(r) 56000 (p56) by stimulating a protein phosphatase, whereas ribulose 5-phosphate inhibited the corresponding protein kinase. In addition, DTT and the calmodulin antagonist trifluoperazine influenced the phosphorylation state of several different polypeptides, indicative of control by redox conditions and a calmodulin-like mediator, respectively. Furthermore, it was established that the phosphorylation of p56 required Mg2+ (> 100-mu-M) whereas that of a polypeptide of M(r) 16000 occurred in the absence of Mg2+ and was inhibited by high concentrations (> 1 mM) of this cation. Several of the phosphopolypeptides detected in vitro corresponded in mobility on SDS-PAGE to species phosphorylated in vivo.