Jul 13, 1976

Structural elucidation and properties of 8alpha-(N1-histidyl)riboflavin: the flavin component of thiamine dehydrogenase and beta-cyclopiazonate oxidocyclase

Biochemistry
D E EdmondsonT P Singer

Abstract

In addition to 8alpha-(N3-histidyl)riboflavin, 8alpha-(N1-histidyl)riboflavin is also formed during the reaction of Nalpha-blocked histidine with 8alpha-bromotetraacetylriboflavin in a yield of 20-25% of the total histidylflavin fraction. The properties of 8alpha-(N1-histidyl)riboflavin are inditical with those of the histidylflavin isolated from thiamine dehydrogenase and beta-cyclopiazonate oxidocyclase but differ from those of 8alpha-(N3-histidyl)riboflavin. These properties include pKa of fluorescence quenching, electrophoretic mobility at pH 5.0, stability to storage, and reduction by NaBH4. Proof for 8alpha substitution is shown by the electron paramagnetic resonance and electron-nuclear double resonance spectra of the cationic semiquinone form, as well as by the proton magnetic resonance spectrum of the oxidized form. The site of histidine substitution by the 8alpha-methylene of the flavin moiety was shown by methylation of the imidazole ring with methyl iodide, cleavage of the methylhistidine-flavin bond by acid hydrolysis at 150 degrees C, and identification of the methylhistidine isomer by electrophoresis. 3-Methylhistidine is the product from the N1-histidylflavin isomer, while 1-methylhistidine is produced from the ...Continue Reading

Mentioned in this Paper

In Vivo NMR Spectroscopy
Semiquinone
Histidine
Protein Methylation
Thiamin oxidase
Borohydrides
Oxidase
Cytokinesis of the Fertilized Ovum
Fluorescence Spectroscopy
Riboflavin

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