Gratuitous induction of xanthine oxidase by 5,6-diaminouracil in continuously grown cells of Arthrobacter globiformis M4

Middelhoven, W.J.; Brons, H.J.; Breedveld, M.W.; Suy, I.M.L.; Plas, H. C. Van Der

doi:10.1007/bf00184983

Cited by 1 publication

(1 citation statement)

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“…First, although ribose-5-phosphate is a glycating agent [37,47], plastids have a repair enzyme to reverse the damage it does [48] and in any case the riboflavin pathway is a negligible source of ribose-5-phosphate compared to the Calvin cycle. Second, the pyrimidines formed from intermediates 1 and 2 appear not to be toxic to microorganisms [49–51]. …”

Section: Discussionmentioning

confidence: 99%

A directed-overflow and damage-control N-glycosidase in riboflavin biosynthesis

Frelin

Huang

Hasnain

et al. 2015

Biochemical Journal

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Plants and bacteria synthesize the essential human micronutrient riboflavin (vitamin B2) via the same multistep pathway. The early intermediates of this pathway are notoriously reactive, and may be overproduced in vivo because riboflavin biosynthesis enzymes lack feedback controls. Here we demonstrate disposal of riboflavin intermediates by COG3236 (DUF1768), a protein of previously unknown function that is fused to two different riboflavin pathway enzymes in plants and bacteria (RIBR and RibA, respectively). We present cheminformatic, biochemical, genetic, and genomic evidence to show that: (i) plant and bacterial COG3236 proteins cleave the N-glycosidic bond of the first two intermediates of riboflavin biosynthesis, yielding relatively innocuous products; (ii) certain COG3236 proteins are in a multienzyme riboflavin biosynthesis complex that gives them privileged access to riboflavin intermediates; and (iii) COG3236 action in Arabidopsis thaliana and Escherichia coli helps maintain flavin levels. COG3236 proteins thus illustrate two emerging principles in chemical biology: directed overflow metabolism, in which excess flux is diverted out of a pathway, and the pre-emption of damage from reactive metabolites.

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