Inhibition of carp liver mitochondrial monoamine oxidase by some commonly-used detergents.

The inhibitory effects of some detergents commonly used in biochemical research on carp liver mitochondrial monoamine oxidase were examined. Sodium dodecylsulfate, octyl-beta-D-glucopyranoside, sodium cholate and Triton X-100 at relatively low concentrations caused strong dose-dependent inhibition of the activity towards tyramine, but digitonin caused only weak inhibition. Sodium dodecylsulfate, octyl-beta-D-glucopyranoside and sodium cholate caused almost complete inhibition of activity in the concentration ranges tested. The extent of inhibition by Triton X-100 was greater after preincubation at 37 degrees C for 30 min than that without preincubation, but with or without preincubation, the inhibition was not substrate-selective and was not complete at a relatively high concentration (2%) of Triton X-100. Without preincubation, the mode of inhibition by Triton X-100 was competitive and reversible with respect to the oxidations of 5-HT, tyramine and PEA, but after preincubation (37 degrees C for 30 min), it became noncompetitive and irreversible, depending on the concentration of detergent used. These findings suggest that it had different actions on the enzyme depending on preincubation. Triton X-100 also slightly changed enzyme sensitivity towards clorgyline and deprenyl, regardless of the preincubation time or the substrate used. Some possible mechanisms of the inhibitory effect of Triton X-100 are discussed.