Transport of folate compounds into Lactobacillus Casei |
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Authors: | G B Henderson F M Huennekens |
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Institution: | Department of Biochemistry, Scripps Clinic and Research Foundation, La Jolla, California 92037 U.S.A. |
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Abstract: | Transport of folate, 5-methyl tetrahydrofolate, and amethopterin into Lactobacillus casei occurs against a concentration gradient, is pH and temperature dependent, requires glucose, exhibits saturation kinetics, is maximal when cells are harvested in late-log phase, and is repressed by excess folate in the growth medium. Km values are 0.35, 0.90, and 0.21 μm for the influx of folate, 5-methyl tetrahydrofolate, and amethopterin, respectively. Dihydrofolate, tetrahydrofolate, 5-formyl tetrahydrofolate, 5-methyl tetrahydrofolate, aminopterin, and amethopterin are inhibitors of folate influx. Countertransport of 5-methyl tetrahydrofolate is enhanced by various other folate compounds. Uptake of folate, 5-methyl tetrahydrofolate, and amethopterin is inhibited to the same degree by increasing concentrations of iodoacetate. These results indicate that a single system is responsible for transport of a variety of folate compounds into L. casei. |
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