Nicotiana glauca invertase: characterization and effects of endogenous alkaloids

Abstract

An acid-soluble invertase from Nicotiana glauca has been studied for the first time. The plant was selected because it is known that the genus Nicotiana has vacuolar alkaloids; the same localization of the acid-soluble invertases in higher plants. The enzyme was partially purified and the optimum pH, Km, Mr, activation energy, fructose effect, activation by protein, sugar specificity, lectin activation were determined. The effects on invertase activity of the alkaloids, nicotine, anabasine and nornicotine present in the plant were also studied. These alkaloids produced a cumulative inhibition of the invertase activity. Other substances like TRIS hydrochloride, pyridoxal hydrochloride and pyridoxine hydrochloride also produced inhibition. All these substances have in common the presence of a quaternary nitrogen atom in their structure. The individual effect of these compounds on the invertase activity appears without meaning as regulators of the enzyme, but their general occurrence may have a role in the functional behaviour of the invertase.