Acetylene Reduction by Nitrogen Fixing Extracts of Clostridium pasteurianum: ATP Requirement and Inhibition by ADP

Abstract

NITROGEN fixing extracts of Clostridium pasteurianum have been shown to catalyse the reduction of acetylene^1,2. The requirements for this reaction were shown to be the same as those for nitrogen fixation, that is, a low potential electron source, ATP, an ATP generating system and magnesium ions. Acetylene reduction provides a more sensitive assay for the activity of the nitrogen fixing system than ammonium production and the measurement of rates of reactions is facilitated. The results described in this communication show that the reduction of acetylene by these extracts can be supported directly by ATP without an ATP generating system. When an ATP generating system is not used we now find that (a) magnesium ions are required for ATP utilization by the nitrogen fixing system, a fact not previously demonstrated, for magnesium ions were required for the ATP-generating system; that (b) the acetylene reduction by the nitrogen fixing system is inhibited by ADP in a manner which suggests that ADP is a negative modifier; and that (c) the acetylene reducing system needs to interact with more than one molecule of ATP.