KINETIC STUDIES OF THE TOXICOLOGICAL EFFECT OF 2,4-DICHLOROPHENOL AND 2,4,6-TRICHLOROPHENOL ON ALKALINE PHOSPHATASE ACTIVITY IN VITRO

摘要

The inhibition kinetic parameters of 2,4-dichloro-phenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) on bovine intestinal mucosa alkaline phosphatase (ALP) activity were studied by spectrophotometry. Both 2,4-DCP and 2,4,6-TCP inhibited ALP activity in a concentration dependent manner, and the 50% inhibitory concentration (/C_(50)) was estimated to be 11.45 mM for 2,4-DCP and 10.20 mM for 2,4,6-TCP, respectively. The apparent Michaelis-Men-ten constant (K_m) and apparent maximum reaction rate (V_(max)) for the hydrolysis of 4-Nitrophenyl phosphate diso-dium salt hexahydrate (p-NPP) was found to be 0.124 mM and 1.80 μM·min~(01), respectively. Both values of K_m and V_(max) decreased distinctly in the presence of 2,4-DCP and 2,4,6-TCP. Lineweaver-Burk plots indicated that the nature of the inhibition was of an uncompetitive type. Kinetic analysis indicated that the values of the inhibition constant (K_i) were estimated to be 9.93 mM for 2,4-DCP and 8.36 mM for 2,4,6-TCP. Therefore, 2,4,6-TCP showed a stronger inhibition effect on ALP activity and displayed a higher affinity for the enzyme-substrate complex than 2,4-DCP.