Kinetics of the inhibition of neurospora invertase by products and aniline

Abstract

The kinetics of the inhibition of the invertase of Neurospora crassa by the products of the hydrolysis, sorbose, and the unusual inhibitor, aniline, have been investigated. The fructosyl transferase activity with glucose or fructose as acceptors of fructose was negligible. The kinetics of the inhibitions were interpreted in terms of a simple three-step mechanism with the enzyme in three forms: free enzyme (E), enzyme-substrate (EFA), and enzyme-fructose (EF). For fructose inhibition of sucrose hydrolysis reciprocal 1 v against 1 S plots showed that the slopes of the lines could be described as a parabolic function of fructose concentration. This was interpreted as nonspecific binding of fructose at the site which normally binds the afructone moiety. The inhibitions by sorbose and aniline were characterized as linear noncompetitive, while that by glucose could be either competitive or noncompetitive, since the effect on the intercepts ( 1 V ) of the lines was at the borderline of experimental error. By contrast, the effect of aniline was mainly on the intercepts of the lines, and was interpreted as a strong combination of aniline with the enzyme-fructose complex, with a much weaker interaction with the free enzyme form.