I'm planning some in vitro experiments to determine if a beta 1-4 glycosidic bond in my molecule of interest is cleaved by the endogenous lysozyme in the human stomach.

I found an abstract from a very old paper ("Lysozyme in human body fluids", by Jan Hankiewicz and Ewa Swierczek in Clinica Chimica Acta Volume 57, Issue 3, 17 December 1974, Page 205) that says, “... lysozyme is present in almost all body fluids, though in different amounts. In serum its activity is normally from 7 to 13 mg/l … A considerable amount of lysozyme was found in gastric juice, about 8 times more than in normal serum” I'm not sure how they arrive at units of “mg/l” as a measure of activity and I also need additional information.

Can anyone here provide information (preferably a pdf of a recent paper) about the abundance, assay and activity of gastric human lysozyme? I've found papers explaining that the amount of human lysozyme is increased in some gastric carcinomas and infections of the GI, but these immunohistological studies don't provide the chemical information I need. I'd be particularly delighted to find an assay that measures degradation of a specific molecule substrate (such as a peptidoglycan) instead of lysis of bacteria.

So, can anyone here tell me how much (human) lysozyme is in a healthy human stomach (mg/ml of gastric fluid) or recommend a biochemical assay for its activity?

Many thanks.

Jamie