type	Journal Article
authors	Palcic, M. M.; Shen, S. J.; Schleicher, E.; Kumagai, H.; Sawada, S.; Yamada, H.; Floss, H. G.
title	Stereochemistry and mechanism of reactions catalyzed by tyrosine phenol- lyase from Escherichia intermedia
journal	Z Naturforsch [C]
Activity	4.1.99.2
ui	87265995
year	(1987)
volume	42
number	4
pages	307-18.
keywords	Carbon Radioisotopes
abstract	Stereochemical studies on tyrosine phenol-lyase from Escherichia intermedia have shown that the alpha, beta-elimination reactions of L- serine and D- and L-tyrosine proceed with retention of configuration at C-beta. Stereospecifically beta-tritiated L-serine is slowly racemized at C-beta. Deuterium from the alpha-position of L-tyrosine is partially transferred to C-4 of the phenol formed when the alpha, beta- elimination reaction is carried out in H2O, although no transfer of alpha-1H in 2H2O was seen. The result favors tautomerization of the p- hydroxyphenyl to a cyclohexadienonyl moiety prior to carbon-carbon bond cleavage. In the conversion of L- to D-alanine catalyzed by tyrosine phenol-lyase, some alpha-hydrogen recycling is observed, pointing to a single-base racemization mechanism. Attempts to demonstrate cofactor motion during racemization by NaBH4 reduction of [3H]PLP-enzyme: D- and L-alanine complexes failed, but showed that, as in other PLP enzymes, the holoenzyme is reduced preferentially from the Re face with respect to C-4' of PLP and enzyme-substrate complexes preferentially from the Si face.
last changed	2002/11/12 16:17