PROTEIN-TYROSINE PHOSPHORYLATION IN THE CYANOBACTERIUM ANABAENA SP STRAIN PCC-7120

Components of a protein tyrosine phosphorylation/dephosphorylation net work were identified in the cyanobacterium Anabaena sp, strain PCC 712 0. Three phosphotyrosine (P-Tyr) proteins of 27, 36, and 52 kDa were i dentified through their conspicuous immunoreactions with RC20H monoclo nal antibodies specific for P-Tyr. These immunoreactions were outcompe ted completely by free P-Tyr (5 mM) but not by phosphoserine or phosph othreonine. The P-Tyr content of the three major P-Tyr proteins and se veral minor proteins increased with their time of incubation in the pr esence of Mg-ATP and the protein phosphatase inhibitors sodium orthova nadate and sodium fluoride, Incubation of the same extracts with [gamm a-P-32]ATP but not [alpha-P-32]ATP led to the phosphorylation of five polypeptides with molecular masses of 20, 27, 52, 85, and 100 kDa. Hum an placental protein tyrosine phosphatase 1B, with absolute specificit y for P-Tyr, liberated significant quantities of P-32(i) from four of the polypeptides, confirming that a portion of the protein-bound phosp hate was present as P-32-Tyr. Alkaline phosphatase and the dual-specif icity protein phosphatase IphP from the cyanobacterium Nostoc commune UTEX 584 also dephosphorylated these proteins and did so with greater apparent efficiency. Two of the polypeptides were partially purified, and phosphoamino analysis identified P-32-Tyr, [P-32] phosphoserine, a nd [P-32]phosphothreonine. Anabaena sp, strain PCC 7120 cell extracts contained a protein tyrosine phosphatase activity that was abolished i n the presence of sodium orthovanadate and inhibited significantly by the sulfhydryl-modifying agents p-hydroxymercuriphenylsulfonic acid an d p-hydroxymercuribenzoate as well as by heparin. In Anabaena sp, stra in PCC 7120 the presence and/or phosphorylation status of P-Tyr protei ns was influenced by incident photon flux density.