EFFECTS OF BENZOPHENANTHRIDINE ALKALOIDS ON THE PHOSPHORYLATION OF ANSIMILAR-TO-44 KDA PROTEIN PRESENT IN A MITOCHONDRIAL-FRACTION OF THE RAT-HEART

Chelerythrine and sanguinarine, benzophenanthridine alkaloids that are known to have a wide variety of biologic actions including inhibitory activity against the phosphorylation of proteins, were tested for the ir effects on the phosphorylation of a specific similar to 44 kDa prot ein present in the mitochondrial fraction of the rat heart. The concen trations required for 50% inhibition were determined to be 90.3 and si milar to 200 mu M for chelerythrine and sanguinarine, respectively, wh ile the median-effect concentrations were 71 and 98 mu M for cheleryth rine and 186 mu M for sanguinarine. The combination index values, dete rmined from median effect plots, for the combination of chelerythrine and taurine in a ratio of 1:100 were greater than 1, which indicates t hat chelerythrine plus taurine is antagonistic. Both chelerythrine and sanguinarine had biphasic (i.e. stimulation and inhibition) effects o n the phosphorylation of the similar to 44 kDa protein. It was determi ned that the biphasic effect for chelerythrine depended upon the time of preincubation at 37 degrees of chelerythrine with the mitochondrial preparation. Preincubation times of 0.5 and 1 min produced 70 and 82% stimulation, while longer preincubation times of 2-22 min resulted in inhibition of the phosphorylation reaction by 40-95%. Dithiothreitol (DTT), a reducing agent, prevented the inhibitory effect of chelerythr ine. Glutathione was less effective in protecting the phosphorylation of the similar to 44 kDa protein. It is suggested that the iminium bon d of chelerythrine reacts with the thiol group on DTT, thereby prevent ing chelerythrine from reacting with thiol groups on the kinase respon sible for phosphorylating the similar to 44 kDa protein. The inhibitor y effects of taurine were only partially eliminated by DTT.