400 - 600 million years ago
||Rubio CA. The Natural Antimicrobial Enzyme Lysozyme is Up-Regulated in Gastrointestinal Inflammatory Conditions. Pathogens. 2014 Jan 16 3(1):73-92. doi: 10.3390/pathogens3010073. p.74 bottom paragraphPubMed ID25437608
|| Sahoo, N.R. Kumar, P. Bhusan, B. Bhattacharya, T.K. Dayal, S. Sahoo, M. Lysozyme in livestock: A guide to selection for disease resistance: A review. J. Anim. Sci. Adv. 2012, 2, 347–360. link
||P.74 bottom paragraph:"During a deliberate search for medical antibiotics, Alexander Fleming [ref 3] discovered lysozyme, one of the natural defense substances against infection. Lysozyme, also known as muramidase
or N-acetylmuramide glycanhydrolase, is a family of enzymes (EC 18.104.22.168), which damage bacterial cell walls by catalyzing hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan, and between N-acetyl-D-glucosamine residues in chitodextrins [ref 4]. Lysozyme, encoded by the LYZ gene [ref 5], is an ancient enzyme whose origin goes back an estimated 400 to 600 million years [primary source]. Linkage studies indicate that the lysozyme M and P genes are present on the same chromosome: calculation from both partial protein sequence and
phylogenetic data indicate that the duplication that gave rise to those genes occurred about 50 million
years ago [ref 5]. Lysozyme is only a generic name (v. gr. lysozyme c is a superfamily composed of 88 distinct lysozymes)."