• 作者： 林萬寅 ; 林耿弘
• 作者服務機構： 台灣大學化學系
• 中文摘要： Stopped-flow radiationless energy transfer experiments have been carried out to investigate the hydrolysis of some dansyl peptide substrates (S) catalyzed by aminopeptidase (E). RET between enzyme tryptophanyl residues and the dansyl group in the substrate allowed direct observation and quantitation of the enzyme-substrate (ES) complexes. Analysis of the stopped-flow RET traces gives K/sub cat/=1.32s/sup -1/ and K/sub M/=47.mu.M for Leu-Ala-NH(CH/sub 2/)/sub 2/ NH-Dns(leu-Ala-DED) and K/sub cat/=4.80s/sup -1/ and K/sub M/=196.mu.M for Leu-Gly-NH(CH/sub 2/)/sub 2/ NH-Dns(Leu-Gly-DED). The activation energies of the enzymatic reactions were determined from the Arrhenius plots to be 57 and 38kJ.bcdot.mol/sup -1/ for Leu-Ala-DED and Leu-Gly -DED, respectively. The kinetic results indicate that the enzyme binds Leu-Ala-DED more tightly than Leu-Gly-DED as revealed by a small value of K/sub M/. That this enzyme catalyzes the turnover of Leu-Gly-DED more efficiently than Leu-Ala-DED is reflected in a large value of K/sub cat/ and a small activation energy. The RET signals during the hydrolysis of Leu-Val-NH(CH/sub 2/)/sub 2/NH-Dns were extremely weak probably because of the inefficient energy transfer in the ES complex or the retention of the product in the enzyme after completion of the reaction. Aminopeptidase was inactive towards the dansyl compounds of the single amino acid studied. This fact may be due to an unfavorable conformation of these compounds in the ES complexes (small K/sub cat/) or a weak binding of the substrates to the enzyme (large K/sub M/) or both.
• 英文摘要： --
• 中文關鍵字： Hydrolysis; Kinetics; Aminopeptidase; Substrate; Stopped-Flow Radiationless Energy Transfer
• 英文關鍵字： 水解作用；動力學；轉胺；受質；基質