The microsomal fraction extracted from grapevine roots obtained from woody cuttings possesses Mg2+-dependent, monovalent cation-stimulated ATPase activity. Addition of BSA, PVPP, choline-Cl, ethanolamine, glycerol-1-P besides EDTA and DTT to the homogenizing medium as preservative compounds was required in order to achieve a successful isolation. When microsomes were extracted according to Hodges and Leonard (1974) by homogenizing root tissue in the presence of EDTA and DTT, the enzyme activity exhibited inhibition by Mg2+ only partially relieved by K+, and properties of acid phosphatase rather than ATPase. Cation-stimulated ATPase of microsomes protected during homogenization was further characterized and it showed optimum activity at pH 7.0 in the presence of Mg2+ plus K+. It was specific as a triphosphatase and Mg2+, rather than other divalent cations, was preferred as a cofactor. As monovalent stimulating cation, only NH4+ could substitute for K+ with equivalent efficiency. The kinetics of K+ stimulation showed a biphasic pattern. Biochemical bases of ion uptake by grapevine seem to be similar to those clarified for annual plants
Extraction and preliminary characterization of microsomal (Mg2++K+)-ATPase activity of grapevine roots
VARANINI, Zeno;
1985-01-01
Abstract
The microsomal fraction extracted from grapevine roots obtained from woody cuttings possesses Mg2+-dependent, monovalent cation-stimulated ATPase activity. Addition of BSA, PVPP, choline-Cl, ethanolamine, glycerol-1-P besides EDTA and DTT to the homogenizing medium as preservative compounds was required in order to achieve a successful isolation. When microsomes were extracted according to Hodges and Leonard (1974) by homogenizing root tissue in the presence of EDTA and DTT, the enzyme activity exhibited inhibition by Mg2+ only partially relieved by K+, and properties of acid phosphatase rather than ATPase. Cation-stimulated ATPase of microsomes protected during homogenization was further characterized and it showed optimum activity at pH 7.0 in the presence of Mg2+ plus K+. It was specific as a triphosphatase and Mg2+, rather than other divalent cations, was preferred as a cofactor. As monovalent stimulating cation, only NH4+ could substitute for K+ with equivalent efficiency. The kinetics of K+ stimulation showed a biphasic pattern. Biochemical bases of ion uptake by grapevine seem to be similar to those clarified for annual plants
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