engleski

Heat inactivation of human serum esterases hydrolysing phenylacetate

The time course of heat inactivation of human serum esterases was studied with phenylacetate as substrate in 0.1 M Tris/HCl buffer pH=8.4 in the absence (total activity) and in the presence of 1.0 mM EDTA (EDTA-insensitive activity). Under these conditions the EDTA-insensitive activity at zero- time inactivation amounted to 2.2 % of the total activity. This in turn means that the total activity is almost completely due to the EDTA-sensitive enzyme(s). The EDTA-insensitive activity remained unaltered up to 30 min. Over the same time interval the EDTA-sensitive activity decreased, and the decrease followed the kinetics of the sum of two first order reactions ; about 80% activity decreased 30-times faster than the remaining 20% activity. This results indicates that human sera contain either two EDTA-sensitive esterases or one esterase in two conformational forms. In either case the EDTA-sensitive phenylacetate hydrolysis can be attributed to the arylesterase (EC 3.1.1.2).

human serum esterases; phenylacetate; heat inactivation

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