Measurements of NAGase Activity in Cow Milk by Fluorescence Method

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Abstract
We examined the correlation between two methods for measuring activities of N-acetyl-β-Dglucosaminidase (NAGase) in cow milk. One was the usual method in which ρ-Nitrophenyl-Nacetyl-β-D-glucosaminide was used as the substrate. The other was the fluorescence method that was tested on microplates in which 4-Methyl-umbelliferyl-N-acetyl-β-D-glucosaminide was used as the substrate. The coefficient correlation and regression equations were r=0.968 and y=0.931 X+1.327 between these methods. The coefficient of variation of simultaneous reproducibility was 4.0%. The average value of NAGase in 125 healthy quarters milk measured by the fluorescence method was 6.2 ±3.3 n mol/min/ml, and that in 275 mastitis quarters 102.6±79.33 n mol/min/ml, statistically higher than the former. In comparison to the other diagnostic methods for mastitis, the coefficient correlation between NAGase and PL test was highest at 0.871, followed by that of direct microscopical somatic cell counts at 0.791, and electrical conductivity at 0.751. According to recovering of mastitis the value of NAGase in milk from mastitis quarters tended to decrease gradually. The Fluorescence method seemed to be simple, useful and a reliable method for diagnosis of mastitis.

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