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 lysozymes are composed of 130 amino acids. The sequences of these two lysozymes 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 cow contains at least three kinds of chicken type lysozymes, that is kidney, milk and stomach lysozymes. The activities of cow and sheep kidney lysozymes were 3% and 29% against Micrococcus luteus at pH 7.0, ionic strength of 0.1 and 30 degrees C, and 57% and 84% against glycol chitin at pH 5.5 and 40 degrees C, which were expressed as percentages relative 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 functioned once as a digestive enzyme in the stomach of an ancestral ruminant.