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 Saccha romyces cerevisiae, (scPPX1) behaves as an adenosine 5'-tetraphosphate phosphohydrolase (EC 3.6.1.14). The hydrolysis of adenosine 5'-tetrap hosphate (p(4)A) to ATP and orthophosphate absolutely depends on one o f the following cations: Co2+ > Mn2+> Mg2+ > Ni2+. Optimum pH is aroun d 4.75 and the K-m for p(4)A estimated at that pH in 5 mM sodium aceta te 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) v alues 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 fo r the hydrolysis of p(4)A. Ammonium molybdate, sodium o-vanadate and z inc 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' adeno sine tetraphosphatases described earlier in rabbit and yellow lupin. ( C) 1998 Elsevier Science B.V.