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Properties of Lactase Produced by Candida pseudotropicalis

Laboratorio de Fermentacion, Centro de Microbiologia y Biologia Celular, Instituto Venezolano de Investigaciones Cientificas (I.V.I.C.), Adpo. 1827, Caracas 1010A, Venezuela

ABSTRACT

Studies were of factors affecting activity of the lactase produced by the yeast Candida pseudotropicalis NCYC 744. The enzyme was inactivated by ethylenediaminetetraacetic acid tetrasodium salt or dialysis against distilled water, and activity was recovered partially upon addition of magnesium⁺⁺ or manganese⁺⁺ salts at optimal concentrations of 10 mM and 1 mM, respectively. Heavy metals and p-chloromercuribenzoate strongly inactivated the enzyme, indicating sulphydryl groups and their requirement for lactase activity. O-nitrophenyl-ß-D-galactopyranoside hydrolysis was inhibited competitively by lactose (inhibition constant 13 mM), methyl-ß-D-galactoside (27 mM), galactose (32 mM), galacturonic acid (160 mM), ribose (175 mM), and galactitol (180 mM); but neither glucose nor melibiose affected enzyme activity. Molecular weight of the lactase was estimated at 200,000. The information will be of significance in the design of processes for lactose hydrolysis with this enzyme.