Episodic evolution in the stomach lysozymes of ruminants.

By sequencing lysozymes c from deer and pig stomachs and comparing them to the known amino acid sequences of other lysozymes c, it was possible to examine the rate of sequence change during and after the period in which this enzyme acquired a new function. Evolutionary tree analysis suggests that the rate went up while lysozyme was being recruited to function as a digestive enzyme in the stomach of early ruminants. Later, presumably after lysozyme was well adapted for functioning in the new environment, which contains acid, pepsin, and fermentation products, the rate of amino acid replacement became subnormal.