Flavin mononucleotide -linked enzyme

Riboflavin (vitamin B2 6.18) consists of an isoalloxazine ring linked to an alcohol derived from ribose. The ribose side chain of riboflavin can be modified by the formation of a phosphoester (forming flavin mononucleotide, FMN, 6.19). FMN can be joined to adenine monophosphate to form flavin adenine dinucleotide (FAD, 6.20). FMN and FAD act as co-enzymes by accepting or donating two hydrogen atoms and thus are involved in redox reactions. Flavoprotein enzymes are involved in many metabolic pathways. Riboflavin is a yellow-green fluorescent compound and, in addition to its role as a vitamin, it is responsible for the colour of milk serum (Chapter 11). 

The structure of the FMN-linked electron carrier, flavodoxin, has been determined from Clostridium MP by Ludwig and co-workers 59,60) and the corresponding protein from Desuljovibrio vulgaris by Jensen and coworkers (61). Rao and Rossmann 4) showed that, with the coordinates available to them, the standard deviation, o-, between these two structures this structure can be compared with the AMP mononucleotide binding unit of LDH and found that o- = 2.4 A for 39 equivalent atoms. When was 2.1 A for 102 equivalent Cn atoms. They also showed that part of these two quite different proteins were so aligned, it became clear that FMN binds to flavodoxin at a site similar to where AMP binds to LDH. Not only is it unlikely that this is an accidental structural relationship, but furthermore Baltscheffsky 62) has supported a common evolutionary origin for flavin and NAD+-linked enzymes on the basis of a comparison of their redox potentials. 

Glycolate which is generated within the chloroplast is exported and further metabolized within the peroxisomes. Here, the flavin mononucleotide (FMN)-linked enzyme glycolate oxidase catalyzes the conversion to... 

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