Lysozyme Assay

Method: The rate of lysis of Micrococcus lysodeikticus is determined as suggested by Shugar (1952). One unit is equal to a decrease in turbidity of 0.001 per minute at 450 nm at pH 7.0 and 25°C under the specified conditions. A wide range of activities are reported for pure lysozyme preparations under these conditions. The Worthington specific activity of 8,000 u/mg dw is equivalent to 50,000 u/mg dw claimed by other suppliers.


  • 0.1 M Potassium phosphate, pH 7.0
  • Micrococcus lysodeikticus cells: Prepare by suspending 9 mg of dried Micrococcus lysodeikticus (Worthington code: ML) cells in 25 ml of 0.1 M potassium phosphate buffer, pH 7.0. Dilute to a final volume of 30 ml with the same buffer.


Dissolve the enzyme at a concentration of one mg/ml in cold reagent grade water. Keep cool until assay. Immediately prior to assay, dilute to a concentration of 150-500 units/ml with reagent grade water. (The rate should fall between 0.015-0.040 ΔA450/minute).


Adjust spectrophotometer to 450 nm and 25°C.

Pipette 2.9 ml of Micrococcus lysodeikticus cell suspension into a cuvette and incubate for 4-5 minutes in order to achieve temperature equilibration and to establish blank rate, if any. Add 0.1 ml of appropriately diluted enzyme to cuvette and record the change in A450 per minute from the initial linear portion of the curve.



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