A sensitive, accurate method has been established for the assay of serum carnosinase by measuring the fluorescence emitted from the L-histidine liberated on treatment with o-phthaldialdehyde. Using this method the serum values for normal adults, infants and children were measured. The mean value was very low in infants of less than 1 year old but increased with age, being almost the same in children aged 6 years or more as in adults. In adult men, the mean activity was 1·85 μmol/mL/h and in adult women it was 2·07 μmol/mL/h. Low activity was observed in patients with muscular dystrophy.
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