RESUMO
Nucleotide-metabolizing enzymes play important roles in the regulation of intracellular and extracellular nucleotide levels. We studied ATPase activity in the nervous ganglia of Phyllocaulis soleiformis, a terrestrial slug. The ATPase was divalent cation-dependent, with a maximal rate for ATP hydrolysis at pH 6.0 and 7.2 in the presence of Ca(2+) (5 mM). Mg(2+)-ATPase activity was only 26% of the activity observed in the presence of Ca(2+) (5 mM). ZnCl2 (10 mM) produced a significant inhibition of 70%. Ca(2+)-ATPase activity was insensitive to the classical ATPase inhibitors ouabain, N-ethylmaleimide, orthovanadate and sodium azide. Levamisole, an inhibitor of alkaline phosphatase, was ineffective. Among nucleotides, ATP was the best substrate. The apparent K(m) ((ATP)) for Ca(2+)-ATPase was 348+/-84 microM ATP and the V(max) was 829+/-114 nmol Pi min(-1) mg(-1) protein. The P. soleiformis ganglial ATPase does not appear to fit clearly into any of the previously described types of Ca(2+)-ATPases.
