Schizosaccharomyces pombe Aps1, a diadenosine 5′,5""-P1,P6-hexaphosphate hydrolase that is a member of the nudix (MutT) family of hydrolases:: Cloning of the gene and characterization of the purified enzyme

The fission yeast Schizosaccharomyces pombe contains a gene on chromosome I that encodes a hypothetical nudix hydrolase, YA9E. The gene, designated aps1, has been cloned and the protein has been purified from Escherichia coli with a yield of 10 mg of Aps1/L of culture. Aps1, composed of 210 amino acids with a calculated molecular mass of 23 724 Da, behaves as a monomer with a sedimentation coefficient of 1.92 S as determined by analytical ultracentrifugation. The effective hydrodynamic radius is about 29 Angstrom as determined by both analytical ultracentrifugation and gel-filtration chromatography. Aps1, whose expression was detected in S. pombe by Western blotting, is an enzyme that catalyzes the hydrolysis of dinucleoside oligophosphates, with Ap(6)A and Ap(5)A being the preferred substrates. The major reaction products are ADP and p(4)A from Ap(6)A and ADP and ATP from Ap(5)A. Values of K-m for Ap(6)A and Ap(5)A are 19 mu M and 22 mu M, respectively, and the corresponding values of k(cat) are 2.0 s(-1) and 1.7 s(-1), respectively. The enzyme has limited activity on Ap(4)A and negligible activity on Ap(3)A, ADP-ribose, and NADH. Aps1 catalyzes the hydrolysis of mononucleotides with decreasing activity in order from p(5)A to AMP. Optimal activity with Ap(6)A as substrate is observed at pH 7.6 and in the presence of 0.1-1 mM MnCl2. Aps1 is the first nudix hydrolase isolated from S. pombe, and it is the first enzyme identified with this specific substrate specificity and reaction products.