Lysozyme, an abomasal enzyme in the ruminants

Area of Science:

• Biochemistry
• Enzymology
• Comparative Physiology

Background:

• Abomasal secretions in ruminants are known to contain various digestive enzymes.
• The presence and specific function of bacteriolytic enzymes in the abomasum have not been fully elucidated.
• Micrococcus luteus is a Gram-positive bacterium susceptible to enzymatic lysis.

Purpose of the Study:

• To identify and characterize the bacteriolytic activity in abomasal secretions of ruminants.
• To determine the enzymatic specificity and properties of the lytic agent.
• To investigate the origin and structural characteristics of the enzyme.

Main Methods:

• Assay of lytic activity against Micrococcus luteus in various secretions.
• Enzyme characterization including specificity (endo-N-acetylmuramoylhydrolase), pH optimum, and molecular weight determination (electrofocusing).
• Immunofluorescence microscopy for localization and amino-acid analysis for structural comparison.

Main Results:

• Strong bacteriolytic activity against Micrococcus luteus was detected exclusively in abomasal secretions.
• The activity was attributed to a glycosidase (lysozyme, EC 3.2.1.17) with endo-N-acetylmuramoylhydrolase specificity, also showing chitinase activity.
• Immunofluorescence confirmed secretion by abomasal gastric glands; electrofocusing revealed a predominant 15,000 Mr form with pH optimum 5.0 and pI 7.5.
• Structural analysis showed homology with known lysozymes, including four disulfide bridges and immunological cross-reactivity among ruminant lysozymes.

Conclusions:

• Abomasal secretions of ruminants, particularly from calves, possess significant bacteriolytic activity due to lysozyme.
• This lysozyme is secreted by gastric glands and exhibits unique biochemical and structural properties.
• The enzyme plays a potential role in the innate immunity and digestive processes within the ruminant abomasum.