THE PRIMARY STRUCTURES AND PROPERTIES OF NON-STOMACH LYSOZYMES OF SHEEP AND COW, AND IMPLICATION FOR FUNCTIONAL DIVERGENCE OF LYSOZYME

Lysozymes were purified from the homogenate of cow and sheep kidneys, and their amino-acid sequences as well as some enzymic properties were determined. Like most mammalian lysozymes both sheep and cow kidney l ysozymes are composed of 130 amino acids. The sequences of these two l ysozymes are the most similar to each other (95% identity), the second most similar to the conventional mammalian lysozymes like human, rat and rabbit lysozymes (74-85% identity), and much less similar to their own stomach lysozymes (65-70% identity). Cow kidney lysozyme is also different from cow milk lysozyme (partial sequence), indicating that c ow contains at least three kinds of chicken type lysozymes, that is ki dney, milk and stomach lysozymes. The activities of cow and sheep kidn ey lysozymes were 3% and 29% against Micrococcus luteus at pH 7.0, ion ic strength of 0.1 and 30-degrees-C, and 57% and 84% against glycol ch itin at pH 5.5 and 40-degrees-C. which were expressed as percentages r elative to hen lysozyme. The net charges of cow and sheep lysozymes at pH 7 were less positive (+1.5 and +2.5, respectively) than human and hen lysozymes (both +8.0) and rather close to the stomach ones (-2 to 0). The decreased net positive charge observed in cow and sheep kidney lysozymes may suggest that the ruminant kidney lysozyme had functione d once as a digestive enzyme in the stomach of an ancestral ruminant.