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Uptake and Metabolism of Riboflavin-5'--D-Glucoside by Rat and Isolated Liver Cells^1,2,

Department of Biochemistry, Emory University, Atlanta, GA 30322-3050

The effect of riboflavin -D-glucoside, isolated from rat liver, on the uptake of riboflavin was studied using freshly isolated rat liver cells. The transport characteristics and metabolic fate of the glucoside were also determined using the radioactive compound. The initial (1-min) uptake of 1 µmol/L [³H]riboflavin glucoside (2.90 ± 0.29 pmol/10⁶ cells) was higher than that of 1 µmol/L [³H]riboflavin (1.35 ± 0.30 pmol/10⁶ cells). However, the accumulation of glucoside after 60 min was significantly lower than that of riboflavin. The presence of up to 30 µmol/L glucoside had no significant effect on the initial uptake of [³H]riboflavin (3 µmol/L, 10⁹ cells/L). Measurement of the kinetic parameters for glucoside gave an apparent K_t value of 83.4 ± 12.4 µmol/L and a V_max of 208.6 ± 17.9 pmol/(10⁶ cells·min). Decreases in the temperature of incubation decreased uptake rate. Replacement of Na⁺ with other monovalent cations did not affect uptake. The presence of D-glucose (1 µmol/L to 5.5 mmol/L) had no inhibitory effect on uptake of 1 µmol/L [³H]riboflavin glucoside. The results indicate that the transport of riboflavin glucoside may not involve the transport mechanisms for riboflavin or D-glucose. Metabolic studies with isolated hepatocytes showed that the glucoside was hydrolyzed to yield riboflavin upon entry into the cell. The vitaminic efficiency of this compound was tested by feeding it to growing male rats. These experiments indicate that the glucoside and free riboflavin are comparable sources of the vitamin.

KEY WORDS: • riboflavin glucoside • rat hepatocytes • flavin transport • flavin metabolism • riboflavin

¹ Supported by the National Institutes of Health (DK 43005) and the Coca-Cola Foundation.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 28 November 1994. Revision accepted 9 March 1995.