Comparative study of catalytic properties in three Tibetan ruminant stomach lysozymes

The stomach lysozymes of ruminants play a paramount role in digestion and offer the chance to probe evolutionary changes in complex organisms on a biochemical basis. In this paper, we focus on the characterization of the catalytic properties of Tibetan ruminant (TR) stomach lysozymes and provide a comparative study of TR stomach lysozymes and nonplateau ruminant stomach lysozymes. The stomach lysozymes were purified with a Carboxymethyl (CM) Sepharose Fast Flow (FF) column and a Bio-Gel P-100 column. The purified stomach lysozymes were characterized by sodium dodecyl sulfate– polyacrylamide gel electrophoresis (SDS–PAGE) and matrix-assisted laser desorption/ionization time-of-flight (MALDITOF) analyses. The antimicrobial activity was evaluated using an agar diffusion method, and the pH, ion strength, temperature, pepsin and trypsin effects on enzymatic activities were evaluated by normal biochemistry methods. The stomach lysozymes of TRs (cattle:TC, yak:TY, and sheep:TS) exhibit maximum activity at pH 5 and ionic strengths below 0.02. TC and TS stomach lysozymes are more resistant to higher temperatures than nonplateau lysozymes. Stomach lysozymes of TRs exhibit greater enzymatic activity than nonplateau lysozymes, in the presence of pepsin and trypsin. Stomach lysozymes from TS retain 86% of their initial enzymatic activity against pepsin inactivation. After trypsin treatment, the stomach lysozymal activities of TRs were significantly affected by trypsin inactivation, with the exception of TS, whose enzymatic activities in the presence of trypsin were 5- and 10-fold higher than those of nonplateau lysozymes. The stomach lysozymes of TRs are more resistant to environmental factors such as pH, temperature, pepsin, and trypsin than nonplateau lysozyme C.