Nonenzymic Formation of Formylisoglutamine

Isolation of formyl-DL-isoglutamine and of isoglutamine from incubations of histidine and urocanate has been reported frequently. The discovery of the nonenzymic reaction now explains its source and helps to resolve a long standing controversy of the dissimilation pathway of histidine. 

It is interesting that the cleavage of the imidazolone ring occurs non-enzymically by a nucleophylic attack of OH at C-2 whereas the enzymic cleavage, also by a nucleophylic attack, occurs at C-4. 

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