The Specific Influence of Acidity on the Mechanism of Nitrogen Fixation by Azotobacter

Publisher Website
Google Scholar
Abstract
The rate of consump-tion of free N gas by Azotobacter vinelandii and by A. chroococcum decreases from a max. at pH 7.8 to a zero limit at 6.0 (5.97 [plus or minus] 0.02). The approach is perpendicular (concave downward) and reversible. Irreversible inac-tivation takes place only below pH 5.0. The rate of consumption of fixed N, viz., urea, NH3, nitrate, decreases from a max. at pH 7.8 to a considerably more acid, measurable limit, at 4.5 or less. The approach is asymptotic (concave upward) and entirely reversible above pH 4.5. The rate of O consumption as a function of pH is similar in type. The limiting value for fixation, pH 6, is a characteristic constant. No factors are known, which are capable of altering this limit; in particular, Ca or Sr conc. and N pressure, factors which, like pH, specifically influence fixation as distinguished from growth or respiration, fail to do so. The Michaelis constant of fixation, KmN2=0.22 atm., or the pressure at 1/2 max. velocity, is independent of pH, and Ca or Sr concentration. Inhibition of fixation by pH and oxalate is non-competitive. The N-fixing enzyme system is termed "azotase" and its known properties are described. The particular enzyme of the system combining directly with N2 is termed "nitrogenase.".

This publication has 4 references indexed in Scilit: