title: Distinct specificities of repressible acid phosphatase from yeast toward phosphoseryl and phosphotyrosyl phosphopeptides.
abstract: By using [32P]-labeled phosphoaminoacids it has been shown that, at mu molar range concentrations, Tyr-32P but neither Ser-32P nor Thr-32P can be significantly dephosphorylated by highly purified repressible acid phosphatase from Saccharomyces cerevisiae. The phosphopeptide Arg-Arg-Ala-Ser(32P)-Val-Ala however, reproducing the phosphorylation site of pyruvate kinase and previously phosphorylated by cAMP-dependent protein kinase, can be very readily dephosphorylated with favourable kinetic constants (Km 0.28 microM, Vmax = 62 units/micrograms) while its derivatives Ala-Ser(32P)-Val-Ala, Arg-Arg-Ala-Thr(32P)-Val-Ala, Arg-Arg-Pro-Ser(32P)-Pro-Ala as well as other peptides and protein substrates phosphorylated by either protein kinase-C or casein kinase-2 are either unaffected or very slowly dephosphorylated by the phosphatase. Conversely Tyr-32P containing angiotensin, poly (Glu, Tyr) 4:1 and the phosphopeptide Asp-Ala-Glu-Tyr(32P)-Ala-Ala-Arg-Arg-Arg-Gly are all dephosphorylated with kinetic constants comparable to those of free phosphotyrosine (Km 0.2-1 microM; Vmax = 4-10 units/micrograms). It is proposed that, while acid phosphatase exhibits a broad specificity toward phosphotyrosine and phosphotyrosyl polypeptides, it is highly selective toward phosphoseryl sites fulfilling definite structural requirements which are reminiscent of those determining phosphorylation by cAMP-dependent protein kinase.
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism*; D000595:Amino Acid Sequence; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D010750:Phosphoproteins / Q000378:metabolism*; D010768:Phosphoserine / Q000378:metabolism; D019000:Phosphotyrosine; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D010750:Phosphoproteins; D010768:Phosphoserine; D019000:Phosphotyrosine; D014443:Tyrosine; D000135:Acid Phosphatase