Role of maltase in the utilization of sucrose by Candida albicans

Two isoenzymes of maltase (EC 3.2.1.20) were purified to homogeneity from Candida albicans. Isoenzymes I and II were found to have apparent molecular masses of 63 and 66 kDa on SDS/PAGE with isoelectric points of 5.0 and 4.6 respectively. Both isoenzymes resembled each other in similar N-terminal sequence, specificity for the α(1→4) glycosidic linkage and immune cross-reactivity on Western blots using a maltase II antigen-purified rabbit antibody. Maltase was induced by growth on sucrose whereas β-fructofuranosidase activity could not be detected under similar conditions. Maltase I and II were shown to be unglycosylated enzymes by neutral sugar assay, and more than 90% of α-glucosidase activity was recoverable from spheroplasts. These data, in combination with other results from this laboratory showing lack of a plausible leader sequence in genomic or mRNA transcripts, suggest an intracellular localization of the enzyme. To establish further the mechanism of sucrose assimilation by maltase, the existence of a sucrose-inducible H⁺/sucrose syn-transporter was demonstrated by (1) the kinetics of sucrose-induced [¹⁴C]sucrose uptake, (2) recovery of intact [¹⁴C]sucrose from ground cells by t.l.c. and (3) transport of 0.83 mol of H⁺/mol of [¹⁴C]sucrose. In total, the above is consistent with a mechanism whereby sucrose is transported into C. albicans to be hydrolysed by an intracellular maltase.