Biochemical properties of the protein tyrosine kinase of the bacterium Acinetobacter johnsonii

The biochemical properties of the autophosphorylating protein tyrosine kina se of Acinetobacter johnsonii were analyzed in vitro, The study shows that the optimal pH value for the phosphorylation reaction is similar to 7. The enzyme activity is stimulated by magnesium and, to a lesser extent, by mang anese ions, whereas calcium ions have no effect. The phosphorylation proces s is rapid reaching a maximum in <2 min, and the enzyme is modified at mult iple sites, Interestingly, the bacterial enzyme is insensitive to a series of molecules known to affect the activity of eukaryotic protein tyrosine ki nases: genistein, quercetin, tosyllysine chloromethyl ketone, and vanadate, We concluded that, even though the overall phosphorylation reaction cataly zed by the A. johnsonii enzyme is identical to that occurring in eukaryotes , this bacterial kinase exhibits a number of specific properties and theref ore probably belongs to a separate group in the general family of protein t yrosine kinases.