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Biochim Biophys Acta. 2004 Mar 9;1661(2):188-95.

Melittin induces both time-dependent aggregation and inhibition of Na,K-ATPase from duck salt glands however these two processes appear to occur independently.

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Department of Biochemistry, School of Biology, M.V. Lomonosov Moscow State University, Moscow 119992, Russian Federation.


Using cupric phenanthroline as a cross-linking agent, we have shown that melittin induced time-dependent aggregations of Na,K-ATPase in microsomal fractions and in preparations of purified Na,K-ATPase from duck salt glands. Incubation of melittin with these preparations also led to the progressive loss of Na,K-ATPase activity. At melittin/protein molar ratio of 5:1, we did not observe inhibition of Na,K-ATPase in the microsomal fraction but the process of enzyme aggregation occurred. At higher melittin/protein molar ratios (10:1 and 30:1), the inhibition of the enzyme and its aggregation proceeded simultaneously but the rates of these processes and maximal values achieved were different. At a melittin/protein ratio of 30:1, Na,K-ATPase inhibition may be described as a biexponential curve with the values for pseudo-first order rate constants being 2.7 and 0.15 min(-1). However, the aggregation may be presented by a monoexponential curve with a pseudo-first order rate constant of 0.15 min(-1). In purified preparations of Na,K-ATPase, the maximal aggregation (about 90%) was achieved at a melittin/protein molar ratio of 2:1, and a further increase in the melittin/protein ratio increased the rate of aggregation but did not affect the value of maximal aggregation. The results show that melittin induced both aggregation and inhibition of Na,K-ATPase but these two processes proceeded independently.

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