Open AccessEvidence for Induced Fit of a Pseudo‐Substrate of Aspartate Aminotransferase
Author(s) -
John Robert A.,
Tudball Norman
Publication year - 1972
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1972.tb02510.x
Subject(s) - chemistry , serine , pyridoxal , enzyme , pyridoxal phosphate , alanine , substrate (aquarium) , formate , active site , catalysis , medicinal chemistry , stereochemistry , biochemistry , amino acid , biology , cofactor , ecology
1 Cytoplasmic aspartate aminotransferase from pig heart catalyses β‐elimination of l ‐serine‐ o ‐sulphate and β‐chloro‐ l ‐alanine. The rates of these reactions have been compared with the rates of the same reactions catalysed by free pyridoxal 5′‐phosphate and CuCl 2 . 2 The effect of formate on the two enzyme‐catalysed reactions has been studied and it has been shown that this anion competitively inhibits the serine sulphate reaction and activates the chloroalanine reaction by increasing k cat considerably. 3 The β‐elimination of both these compounds is accompanied by progressive inactivation of the enzyme but whereas formate decreases the rate of inactivation by serine sulphate it increases the rate of inactivation by chloroalanine. 4 It is proposed that formate binds to the active site of the enzyme in a position normally occupied by the β‐carboxyl group of aspartate, the carboxyl group of glutamate or the sulphate group of serine sulphate and that binding of the appropriate anion induces a change in the active site which accounts simultaneously for increased catalytic activity and increased inactivation.