Urinary lumichrome-level catabolites of riboflavin are due to microbial and photochemical events and not rat tissue enzymatic cleavage of the ribityl chain
Oka, M.; McCormick, D.B.
Journal of Nutrition 115(4): 496-499
1985
ISSN/ISBN: 0022-3166 PMID: 3981268 Document Number: 261521
The occurrence of 7- and 8-carboxylumichromes as a significant fraction of riboflavin-derived material in rat urine has led to a re-examination of tissues for possible enzymic activity that could contribute to cleavage at position 10 of the D-ribityl chain of the vitamin. For this, homogenates were incubated in the dark in different conditions with pure [2-14C]riboflavin with and without cofactors before extractions with phenol for flavins or chloroform for lumichromes, and high-pressure liquid chromatography was used to separate and to quantitate all radioactive compounds. Only unmodified riboflavin and small amounts of FMN were found even though the level of detection of known derivatives, including 10-(2'-hydroxyethyl)flavin and lumichrome, was extremely sensitive. Hence, rat tissue per se does not seem responsible for significant cleavage of the D-ribityl chain of riboflavin. Rather, such cleavage to the lumichrome level must result from the known actions of intestinal microflora and potentially from photolysis.