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Kinetics of proton transfer reactions of lysozyme with p ‐nitrophenol near neutral pH—a study of dynamic properties of Glu 35 and His 15
Author(s) -
Segawa ShinIchi,
Husimi Yuzuru,
Wada Akiyoshi
Publication year - 1975
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1975.360141003
Subject(s) - chemistry , lysozyme , proton , kinetics , nitrophenol , reaction rate constant , stereochemistry , medicinal chemistry , organic chemistry , catalysis , biochemistry , physics , quantum mechanics
Kinetics of proton transfer between lysozyme and a pH indicator p ‐nitrophenol ( p ‐Np) were measured by the temperature‐jump method in a pH range of 6.0–7.0. Two well‐defined relaxation processes were observed. The fast process (τ ≃ 15 μsec) was also observed for a lysozyme derivative succinylated at the terminal α‐amino group of Lys 1. Therefore, the fast process was found to be attributable to the proton transfer reaction of His 15 with p ‐Np. The slow process (τ ≃ 50 μsec) was found to be characteristic of the proton transfer reaction of Glu 35, because it disappeared completely in solution containing a lysozyme derivative having an ester crosslink between the carboxyl group of Glu 35 and indol C‐2 of Trp 108. The rate constants for proton transfer from Glu 35 and His 15 to p ‐Np were found to be 9 × 10 6 /sec/M (±65%, 23°C) and 3 × 10 8 /sec/M (±20%, 25°C), respectively. These data indicate that the proton of the carboxyl group of Glu 35 is kinetically stabilized in lysozyme.