Muraki M, Morikawa M, Jigami Y, Tanaka H
National Chemical Laboratory for Industry, Yatabe, Ibaraki, Japan.
Biochim Biophys Acta. 1987 Nov 5;916(1):66-75. doi: 10.1016/0167-4838(87)90211-1.
In order to probe the roles of Tyr-63, Trp-64 and Trp-109 in the active site of human lysozyme (peptidoglycan N-acetylmuramoylhydrolase, EC 3.2.1.17), six human lysozymes containing a mutation, Tyr-63 to Leu, Trp-64 to Phe or Tyr, Trp-109 to Phe or Tyr, and Glu-35 to Asp, were newly synthesized and their immunological and enzymatical activities were examined in comparison with the native enzyme. Enzymatic characterization indicated: (i) that the existences of an aromatic residue at position 63 and a tryptophan residue at position 64 are essential for the effective hydrolysis of glycol chitin substrate, but not for the lysis of bacterial substrate; (ii) that the conversion of Trp-109 to Phe or Tyr reduces the maximal velocity of the lytic reaction to 25% of the wild-type enzyme; however, the apparent affinity constant is not affected. Further, the difference between the activity against the charged substrate and that against the non-charged substrate was discussed from a viewpoint of the electrostatic interaction between enzyme and substrate.
