Influence of pN2 and pD2 on HD formation by various nitrogenases

Abstract
Formation of HD from D2 was demonstrated with nitrogenase preparations from Azotobacter vinelandii, Clostridium pasteurianum, Klebsiella pneumoniae and Azospirillum sp. The formation of HD from D2 is a general property of nitrogenases. The nitrogenases differ in their Ki values for D2 (N2 fixation) and in their rates of catalyzing HD formation; among the nitrogenases tested, C. pasteurianum nitrogenase had the lowest activity for formation of HD. When contaminating N2 was removed from the atmospheres above reaction mixtures, less than 1% of the total electron flux in the system was directed to HD formation; N2-independent HD formation is apparently not significant. A working hypothesis is suggested that operates without invoking an N2-independent reaction for forming HD.