The kinetics of glucose liberation from lactose by b-galactosidase from A. niger was studied in a wide range of the main variables. The anal. shows that the kinetic models proposed so far are not adequate. The main finding is that the reaction rate is not linearly correlated to the enzyme concn.; it increases more than proportionally. This nonlinear relation results because this lactase can distinguish between a- and b-galactose. a-Galactose acts as competitive and anticompetitive inhibitor, whereas b-galactose is a competitive one. The competitive inhibition of the a-anomer is .apprx.12 times more severe than that of the b-anomer. The kinetics, including a simplified model for the mutarotation of galactose is given for a temp. of 50 Deg at a pH of 3.5, the most likely conditions for the application of this lactase in acid whey treatment. [on SciFinder (R)]