Open AccessChorismate Mutase from Euglena gracilis
Author(s) -
Weber Hermann L.,
Böck August
Publication year - 1970
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1970.tb01078.x
Subject(s) - chorismate mutase , euglena gracilis , tryptophan , enzyme , biochemistry , phenylalanine , enzyme kinetics , cooperativity , tyrosine , chemistry , biology , stereochemistry , biosynthesis , active site , amino acid , chloroplast , gene
One of the key enzymes in the regulation of aromatic acid biosynthesis, chorismate mutase, has been purified about 3000‐fold from cell‐free extracts of Euglena gracilis . The enzyme possesses an apparent molecular weight of 160 000. Judged by our criteria Euglena possesses only one species of chorismate mutase. The purified enzyme is sensitive to inhibition by tyrosine and phenylalanine and to activation by tryptophan; the extent of inhibition and activation is strictly pH‐dependent. The inhibition by phenylalanine and by tyrosine is partially competitive with chorismate. Substrate saturation data of the effector‐free enzyme analyzed by the Hill equation yield values of n of 2.0 at pH 8.4 and of close to 1.0 at pH 7.0, thus indicating strong cooperative interactions under the former and little or no interactions under the latter condition. At pH 7.0 the presence of the inhibitors results in an increase of the value of n suggesting cooperativity under this condition. Little or no cooperative interaction between the inhibitor sites was observed ( n′ = 1.2). In the presence of tryptophan chorismate mutase exhibits strict Michaelis kinetics ( n = 1.0 at pH 7.0 and 8.4).