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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Keywords Melittin, Na, K-ATPase, Protein aggregation
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Journal Biochimica et Biophysica Acta - Biomembranes
Shorina, E.A. (Ekaterina A.), Dolgova, N.V. (Nataliya V.), Rubtsov, A.M. (Alexander M.), Storey, K, & Lopina, O.D. (Olga D.). (2004). Melittin induces both time-dependent aggregation and inhibition of Na,K-ATPase from duck salt glands however these two processes appear to occur independently. Biochimica et Biophysica Acta - Biomembranes, 1661(2), 188–195. doi:10.1016/j.bbamem.2004.01.003