[Determination of leucine aminopeptidase in cow's milk]

Reported in this paper are studies into the applicability of the Fermognost LAP test set (VEB Arzneimittelwerke Dresden) to the measurement of leucine-aminopeptidase activity (LAP) in milk and blood serum of cows. Testing of optimum measuring conditions under which to use the enzyme assay method in milk checks revealed that the LAP test set can be used for LAP activity measurement of milk and blood serum of cows, provided proper preparation of the milk and due consideration of other testing approaches. Colorimetric measurement is made in cuvettes, with 0.1 cm in layer thickness. Dilution or storage of milk samples is not permissible, since changes in enzyme activity are of incidental nature. LAP activities between 4 U/l and 150 U/l were recorded from 280 milk samples. Variation recorded for milk from clinically intact udder quarters was between 4 U/l and 35 U/l, as established by comparison of various parameters, such as cell count, chloride, and lactose. An upper limit value of 40 U/l was derived from that variation. Reproducibility of that enzyme assay method for milk was V = 2.8 per cent, S = +/-0.7 U/l. The milk enzyme was inhibited by chelate formers and activated by Mn2+ ions. LAP activities between 5 U/l and 37 U/l were recorded from 28 blood sera of cattle and gave a mean value of 14 U/l. No regular relationship was found to exist between LAP activities in milk from various udders, and in blood serum of cattle.