Unique Ca2+-activated ATPase in the nervous ganglia of Phyllocaulis soleiformis (Mollusca) |
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Institution: | 1. Istituto Zooprofilattico Sperimentale del Lazio e della Toscana “M. Aleandri”, Via Appia Nuova 1411, 00178 Roma, Italy;2. Faculty of Veterinary Medicine, University of Teramo, Piazza Aldo Moro 45, 64100 Teramo, Italy;3. Giardino Zoologico di Pistoia, Via Pieve a Celle 160, 51100 Pistoia, Italy;4. Department of Animal Medicine, Production and Health, University of Padova, Viale dell''Università 16, 35020, Legnaro, (Padova), Italy |
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Abstract: | 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 Ca2+ (5 mM). Mg2+-ATPase activity was only 26% of the activity observed in the presence of Ca2+ (5 mM). ZnCl2 (10 mM) produced a significant inhibition of 70%. Ca2+-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 Km (ATP) for Ca2+-ATPase was 348±84 μM ATP and the Vmax 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 Ca2+-ATPases. |
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