Jun 10, 1976

Transport of riboflavin into yeast cells

The Journal of Biological Chemistry
M PerlT P Singer

Abstract

Riboflavin-requiring mutants of Saccharomyces cerevisiae are able to transport 14C-labeled riboflavin into the cell, although no significant transport is seen in commercial yeast or in the parent strain from which the mutants were derived. Transport activity is greatest in the early to mid-log phase of anaerobic growth and declines sharply in the late log phase. In aerobically grown cells activity is substantially lower at all stages of growth. In the assay devised for its measurement, transport activity shows a sharp pH optimum at pH 7.5, a strong temperature dependence (EA = 23,100 cal/mol), and saturation kinetics with respect to riboflavin (Km = 15 muM), characteristics consistent with a carrier-mediated mechanism. Monovalent inorganic cations, particularly K+ and Rb+, stimulate riboflavin uptake, while certain organic cations are inhibitory. Besides riboflavin only 7-methylriboflavin, 8-methylriboflavin, and 5-deazaflavin have been found to serve as substrates, while lumiflavin, tetraacetylriboflavin, and N10-[4'-carboxybutyl]-7,8-dimethylisoalloxazine do not, although a number of flavin analogs in which the ribityl side chain is modified are good competitive inhibitors of riboflavin uptake. Compounds resembling the ribity...Continue Reading

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Mentioned in this Paper

Thermodynamics
Potassium
Glucose, (beta-D)-Isomer
Riboflavin
Calorimetry
Cell Division Phases
Anaerobiosis
Cations, Monovalent
Flavins
Saccharomyces cerevisiae

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