TYROSINE PHOSPHORYLATION OF A CYTOPLASMIC PROTEIN FROM THE ANTARCTIC PSYCHROTROPHIC BACTERIUM PSEUDOMONAS-SYRINGAE

Cytoplasmic proteins from the antarctic psychrotrophic bacterium Pseud omonas syringae showed two phosphorylated proteins of molecular mass 6 6 kDa and 62 kDa. The phosphorylation of 66 kDa protein was enhanced i n the presence of Triton X-100 solubilised membrane proteins at a high er temperature (30 degrees C) only. Western blot analysis and phosphoa mino acid analysis indicated that the 66 kDa protein is phosphorylated at a tyrosine residue. Surprisingly, sodium orthovanadate, which is a known phosphotyrosine phosphatase (PTPase) inhibitor, inhibited the p hosphorylation of the protein. The possible importance of this tyrosin e phosphorylated protein to growth at low temperature is suggested.