| Autor: |
PETKOV, Dimiter, CHRISTOVA, Evdokia, POJARLIEFF, Ivan, STAMBOLIEVA, Nikolina |
| Předmět: |
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| Zdroj: |
European Journal of Biochemistry; Feb75 Part 1, Vol. 51 Issue 1, p25-32, 8p |
| Abstrakt: |
The absence of both nonproductive binding and substrate activation and also the good solubility of the substrates make the urokinase-catalysed hydrolysis of specific anilides a very suitable reaction for substrate structure-enzyme activity studies. Derivatives of α-N-acetyl-L-lysine anilide with high σ--value substituents in the aniline ring were synthesized. Rate constants kcat. and apparent Michaelis-Menten constants Km(app.) are presented. From the substituent dependence of kcat. and from the fact that kcat. is 13 to 37 times smaller than the deacylation rate constant it is concluded that the rate-limiting step proceeds prior to deacylation. The catalytic rate constant kcat. obeys a linear free-energy relationship of the Hammett type with Q = + 0.72. Two different mechanisms implied by the results obtained from the model reaction (specific base and general acid-base catalysed hydrolysis of N-acetylglycine anilides under extreme conditions) are proposed in order to account for this positive and low q-value. In the first mechanism the breakdown of an enzyme tetrahedral intermediate is rate-limiting, while in the second one its formation controls the overall rate. The discrimination between the two mechanisms, however, could not be found. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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