H. Heymann et S. Gunther, CALCULATION OF SUBSITE AFFINITIES OF HUMAN SMALL-INTESTINAL GLUCOAMYLASE-MALTASE, Biological chemistry Hoppe-Seyler, 375(7), 1994, pp. 451-455
Several years ago, Hiromi at al. (1973) Biochim. Biophys. Acta 302, 36
2-375 proposed a theory for the action patterns of glucoamylases, base
d on data from steady-state kinetics. The Michaelis-Menten constants (
K-m) and the turnover number for maltooligosaccharides were used to ev
aluate the subsite affinities. We have now used this method for evalua
ting the subsite affinities for glucoamylase(EC 3.2.1.3)-maltase (EC 3
.2.1.20) from human intestinal mucosa. For calculation of the subsite
affinities, A(1) and A(2), and the intrinsic rate constant k(int), we
use a modified algorithm and a computer program for nonlinear least sq
uare fitting. Considerable substrate inhibition was shown by maltotrio
se, minor inhibition by maltotetraose, and no inhibition by maltose an
d the other maltooligosaccharides. This indicates a more complex kinet
ic behaviour of the enzyme with respect to maltotriose. Evaluation of
the subsites reveals that A(2) is the main binding site (18.1 kJ/mol),
whereas the other affinities, with the exception of A(1), are lower t
han 2.5 kJ/mol.