Acetylene as a competitive inhibitor of N-2 fixation.

Abstract

A variety of gases, including H2, CO, N20, and NO, competitively inhibit N2 fixation.'Sch6llhorn and Burris2 and Dilworth3 independently observed that acetylene also inhibits N2 fixation, and Schollhorn and Burris2 reported that the inhibition is competitive.Dilworth3 observed that acetylene is reduced to ethylene by extracts from Clostridium pasteurianum.Methods and Materials.-Thegases H2, N2 (high purity), and acetylene (purified grade) were commercial cylinder gases.Acetylene was freed from traces of acetone by condensing the ace- tone in a trap cooled with dry ice.Enzyme preparations: Cultures of Clostridium pasteurianum (strain W-5) were grown in a nitrogen-deficient medium with N2, harvested, dried in a rotary evaporator, and stored in evacu- ated tubes at -20°.Extracts were obtained by autolyzing the dried cells for 1 hr with shaking in 0.05 M cacodylate buffer pH 6.8 at 320 in an atmosphere of H2.The resulting suspension was centrifuged at 20,000 g for 25 min, and the supernatant was used.Azotobacter vinelandii (strain 0) was grown in aerated liquid cultures in 180-liter glass-lined fermentors, and the cells were stored as a frozen paste.N2-fixing extracts were prepared as de- scribed by Bulen, Burns, and LeComte4 and the supernatant of successive centrifugations at