Effects of benzophenanthridine alkaloids on the phosphorylation of an approximately 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 their effects on the phosphorylation of a specific approximately 44 kDa protein present in the mitochondrial fraction of the rat heart. The concentrations required for 50% inhibition were determined to be 90.3 and approximately 200 microM for chelerythrine and sanguinarine, respectively, while the median-effect concentrations were 71 and 98 microM for chelerythrine and 186 microM for sanguinarine. The combination index values, determined from median-effect plots, for the combination of chelerythrine and taurine in a ratio of 1:100 were greater than 1, which indicates that chelerythrine plus taurine is antagonistic. Both chelerythrine and sanguinarine had biphasic (i.e. stimulation and inhibition) effects on the phosphorylation of the approximately 44 kDa protein. It was determined that the biphasic effect for checlerythrine 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 chelerythrine. Glutathione was less effective in protecting the phosphorylation of the approximately 44 kDa protein. It is suggested that the minimum bond of chelerythrine reacts with the thiol group on DTT, thereby preventing chelerythrine from reacting with thiol groups on the kinase responsible for phosphorylating the approximately 44 kDa protein. The inhibitory effects of taurine were only partially eliminated by DTT.