ENHANCEMENT OF ADENYLATE-CYCLASE ACTIVITY IN S49 LYMPHOMA CELL-MEMBRANES BY THE TOXIN THIONIN PYRULARIA-PUBERA

We investigated the mode of action of Pyrularia thionin on adenylate c yclase in S49 lymphoma cell membranes. Thionin increased the forskolin -induced cAMP production in both wild-type and cyc(-) variant cell mem branes. Thionin increased the apparent efficacy, but not potency, of t he stimulation of adenylate cyclase by forskolin. Our results also ind icated that the stimulatory G protein (G(s)) was not involved in the a ction of thionin on adenylate cyclase; however, thionin appeared to re duce the effect of G(i) on adenylate cyclase. We examined the effect o f thionin on the temperature dependence of adenylate cyclase activity. The effect of thionin was not quantitatively the same at all temperat ures. The effect was greatest in the range of about 30 degrees C to 50 degrees C. In addition, cardiotoxin, a structurally distinct peptide that alters the properties of biological membranes similarly to thioni n, also enhanced the activity of adenylate cyclase. It seems reasonabl e to suspect that thionin influences the activity of adenylate cyclase indirectly by acting on the membrane.