Ectoenzymatic breakdown of diadenosine polyphosphates by Xenopus laevis oocytes.

摘要: Xenopus laevis oocytes exhibit ectoenzymatic activity able to hydrolytically cleave extracellular diadenosine polyphosphates (Ap(n)A). The basic properties of this ectoenzyme were investigated using as substrates di-(1,N(6)-ethenoadenosine) 5',5"'-P(1),P(4)-tetraphospate [epsilon-(Ap(4)A)] and 5',5"'-P(1),P(5)-pentaphospate [epsilon-(Ap(5)A)], fluorogenic derivatives Ap(4)A Ap(5)A, respectively. epsilon-(Ap(4)A) epsilon-(Ap(5)A) are hydrolysed by folliculated according hyperbolic kinetics with K(m) values 13.4 12.0 microM Vmax 4.8 5.5 pmol per oocyte min, is activated Ca(2+) Mg(2+), reaches maximal at pH 8--9 inhibited suramin. Defolliculated also hydrolyse both similar but V(max) approximately doubled respect controls. Chromatographic analysis indicates that first cleaved into 1,N(6)-ethenoAMP (epsilon-AMP) + 1,N(6)-ethenoATP (epsilon-ATP) epsilon-AMP 1,N(6)-ethenoadenosine tetraphosphate (epsilon-Ap(4)), respectively, which catabolized (epsilon-Ado) the end product oocytes. Denuded oocytes, however, show a drastically reduced rate epsilon-Ado production, being main end-product epsilon-(Ap(n)A) catabolism. Results indicate that, whereas Ap(n)A-cleaving appears be located mainly in oocyte, ectoenzymes involved dephosphorylation mononucleotide moieties follicular cell layer.