[Active transport of riboflavin in the yeast Pichia guilliermondii. Detection and some properties of the cryptic riboflavin permease].

In contrast to cells and protoplasts of the wild strain intact cells and protoplasts of riboflavin (RF)-deficient mutants of Pichia guilliermondii yeast possessing multiple sensitivity to antibiotics and antimetabolites were found capable to accomplish active transport of RF. The accumulation of RF against concentration gradient was energized by endogenous energy sources and was strongly depressed by uncouplers of oxidative phosphorylation and by inhibitors of respiration. RF transport was also blocked by the agents which destroy the permeability barrier and by sucrose. Cyclohemide did not inhibit the transport of vitamin B2. Uptake of RF depends on temperature and pH of the incubation mixture. RF permease possessed rather stringent substrate specificity and did not catalyze transport of FMN and FAD. RF uptake in two strains tested, MS1-3 and MS1, followed saturation kinetics (Km = 0.17 mM and 2.0 mM, respectively) and was not connected with RF auxotrophy. The ability for exogenous RF uptake was controlled by recessive allele. Restoration of normal resistance to antibiotics and antimetabolites was accompanied by a decrease in the permease affinity for substrate.