Reversible reaction via a carbanion intermediate in the elimination of ammonia from L-histidine catalysed by histidine ammonia-lyase.
L-[5'-2H2]Histidine was used as a substrate to investigate the enzymatic reaction mechanism with histidine ammonia-lyase from Pseudomonas fluorescens. The study was performed to determine the exchange rate of deuterium at C-5' of the imidazole ring with solvent hydrogen relative to the net urocanic acid production. The extent of hydrogen exchange at C-5' of histidine or urocanic acid was measured by gas chromatography-mass spectrometry-selected ion monitoring, monitoring the molecular ion intensities of the respective gas chromatographic derivatives, at m/z 380 and 379 for histidine and at m/z 267 and 266 for urocanic acid. The observed hydrogen exchange at C-5' suggested a reversible mechanism via a carbanion intermediate in the reaction with histidine ammonia-lyase.
Furuta
T
T
Tokyo College of Pharmacy, Japan.
Takahashi
H
H
Kasuya
Y
Y
D000641:Ammonia / Q000737:chemistry*; D000642:Ammonia-Lyases / Q000378:metabolism*; D002384:Catalysis; D008401:Gas Chromatography-Mass Spectrometry; D006639:Histidine / Q000032:analysis / Q000737:chemistry*; D007553:Isotope Labeling; D011551:Pseudomonas fluorescens / Q000201:enzymology; D014560:Urocanic Acid / Q000032:analysis
D006639:Histidine; D000641:Ammonia; D000642:Ammonia-Lyases; D014560:Urocanic Acid