Adenosine 5′-tetraphosphate phosphohydrolase activity is an inherent property of soluble exopolyphosphatase from yeast Saccharomyces cerevisiae

Homogeneous soluble exopolyphosphatase (EC 3.6.1.11) from yeast Saccharomyces cerevisiae, (scPPX1) behaves as an adenosine 5'-tetraphosphate phosphohydrolase (EC 3.6.1.14). The hydrolysis of adenosine 5'-tetraphosphate (p(4)A) to ATP and orthophosphate absolutely depends on one of the following cations: Co2+ > Mn2+> Mg2+ > Ni2+. Optimum pH is around 4.75 and the K-m for p(4)A estimated at that pH in 5 mM sodium acetate and at 5 mM CoCl2 is 80 +/- 10 mu M. Adenosine 5'-pentaphosphate (p(5)A) is degraded under these conditions Is-fold more slowly than p(4)A. Assuming that the mass of scPPX1 is 45 kDa, the calculated k(cat) values for p(4)A and for p(5)A are 723 and 40 s(-1), respectively. Two other nucleoside 5'-tetraphosphates (p(4)N), guanosine tetraphosphate (p(4)G) and inosine tetraphosphate (p(4)I), were hydrolyzed to P-i and either GTP or ITP, respectively, at the same rate as that observed for the hydrolysis of p(4)A. Ammonium molybdate, sodium o-vanadate and zinc chloride inhibit the hydrolysis of p(4)A (I-50 values are 0.08, 0.3 and 0.4 mM, respectively). This newly recognized 'acidic' adenosine tetraphosphatase activity from yeast is compared with two 'pH 8' adenosine tetraphosphatases described earlier in rabbit and yellow lupin. (C) 1998 Elsevier Science B.V.