Modification of neuroblastoma X glioma hybrid NG108-15 adenylate cyclase by vanadium ions

Vanadium ions activate as well as inhibit the activity of the NG108-15 adenylate cyclase in vitro in the absence of any hormone. Below 5mM ion, ortho- and metavanadate activate; the maximal increase in activity is 2-fold. Vanadyl sulfate, at 0.1-0.1mM, activates to a similar magnitude as does vanadate over these concentrations; above 0.1mM, it inhibits. Activation of the enzyme by vanadate is not additive to that induced by PGE₁ or NaF. Vanadium ions do not alter the Ka for PGE₁-activation, nor the Ki for Dala met amide-inhibition, nor diminish the efficacy of opiate, muscarinic and alpha adrenergic regulation of the enzyme. However, the mechanisms by which NaF and vanadium ions activate must differ. Vanadium, unlike NaF, does not attenuate the ability of hormone receptors to direct inhibition of adenylate cyclase.