Selective inhibition of .gamma.-aminobutyric acid aminotransferase by (3R,4R), (3S,4S)- and (3R,4S), (3S,4R)-4-amino-5-fluoro-3-phenylpentanoic acids
作者:Richard B. Silverman、Shrenik M. Nanavati
DOI:10.1021/jm00165a008
日期:1990.3
(3R,4R),(3S,4S)- and (3R,4S),(3S,4R)-4-amino-5-fluoro-3-phenylpentanoic acid (1a and 1b) were synthesized and studied as selective inactivators of gamma-aminobutyric acid (GABA) aminotransferase. Neither compound caused time-dependent inactivation of the enzyme. Neither compound underwent enzyme-catalyzed transamination nor was fluoride ion eliminated from either compound by the enzyme. No 3-phenyllevulinic acid, the product of elimination of HF followed by enamine hydrolysis, was detected. However, both 1a and 1b were competitive reversible inhibitors of GABA aminotransferase; the Ki for 1a was smaller than the Km for GABA. These results suggest that 1a and 1b bind to the active site of GABA aminotransferase, but gamma-proton removal does not occur. Whereas (S)-4-amino-5-fluoropentanoic acid (AFPA) is a potent inhibitor of L-glutamic acid decarboxylase (GAD), neither 1a nor 1b at concentrations 40 times the Ki of AFPA caused any detectable competitive inhibition of GAD. Therefore, the incorporation of a phenyl substituent at the 3-position of AFPA confirms selective inhibition of GABA aminotransferase over GAD.
(3R,4R),(3S,4S)-和(3R,4S),(3S,4R)-4-氨基-5-氟-3-苯基戊酸(1a和1b)被合成并研究为γ-氨基丁酸(GABA)氨基转移酶的选择性失活剂。两种化合物均未引起酶的时间依赖性失活。两种化合物均未发生酶催化的转氨作用,且酶未从两种化合物中消除氟离子。未检测到3-苯基左旋天冬氨酸,这是HF消除后烯胺水解的产物。然而,1a和1b均为GABA氨基转移酶的竞争性可逆抑制剂;1a的Ki小于GABA的Km。这些结果表明,1a和1b结合到GABA氨基转移酶的活性位点,但γ-质子消除没有发生。而(S)-4-氨基-5-氟戊酸(AFPA)是L-谷氨酸脱羧酶(GAD)的强效抑制剂,但1a和1b在浓度为AFPA的Ki值40倍时未引起GAD的可检测竞争性抑制。因此,AFPA在3位引入苯基取代基证实了对GABA氨基转移酶相对于GAD的选择性抑制。