Lysozyme is normally present in plasma (5.9 mg/l) but only in trace amounts in urine. In certain renal disorders, urinary excretion of lysozyme is significantly increased, which could be of diagnostic significance (Harrison, J.F.; Parker, R.W. and De Silva, K.L., J. Clin. Pathol., 26, 278, 1973). Analysis of serum lysozyme levels could also be used as a diagnostic tool in acute and chronic myelocytic leukemia and in acute lymphocytic leukemia (Grossowicz, N.; Ariel, M. and Weber, T., Clin. Chem., 25, 484, 1979).

1. 0.1 M Potassium phosphate buffer, pH 6.24.
2. Micrococcus lysodeikticus suspension (substrate). Suspend 9 mg of dried Micrococcus lysodeikticus cells in 25 ml of 0.1 M Potassium phosphate buffer, pH 6.24. Dilute to a final volume of 30 ml with the same buffer.
3. Lysozyme (enzyme) solution. Dissolve enzyme in 0.1 M phosphate buffer to yield a concentration of 1 mg/ml. Keep refrigerated. Using potassium phosphate buffer as solvent, dilute this stock enzyme solution to yield a concentration of 100-200 U/ml. Prepare fresh immediately prior to assay.

1. Set spectrophotometer (equipped with strip chart recorder and temperature control) at 450 nm and 25°C.
2. Into a cuvette, pipette 2.9 ml Micrococcus lysodeikticus suspension and incubate in spectrophotometer at 25°C for 5 minutes.
3. Calculate the decrease in absorbance at 450 nm per minute (µE450 nm/min).