In vitro degradation of the stereoisomers of soman in guinea-pig, mouse and human skin

Abstract The fate of the four stereoisomers of soman [C(−)P(+), C(+)P(+), C(+)P(−) and C(−)P(−)] was studied by incubating 10 μM C(±)P(±)-soman at pH7.4 and 37° for various periods in the presence or absence of homogenates (1:10 and 1:20 w/v) of guinea-pig, mouse or human skin. The remaining concentrations of the soman isomers were determined gas chromatographically. Similar rates of spontaneous (non-enzymatic) hydrolysis ( K = 0.005 min −1 ) were found for the four isomers of soman. Hydrolysis of the toxic (C(±)P(−)-isomers is not accelerated in the presence of the skin homogenates. In contrast, the non-toxic C(±)P(±)-isomers are enzymatically hydrolysed. As the amount of proteins present in the homogenates varied the rate constants for enzyme hydrolysis per protein concentration were calculated. Except for the high hydrolysis rate constant of > 0.127/min.g.l for C(+)P(+) in human skin, these values were almost similar (0.031–0.045/min.g.l) for the skin homogenates tested. Irreversible binding sites for the four soman-stereoisomers are only found in homogenates of mouse skin; 122–195 pmol soman-isomer are bound per mg protein. After preincubation of mouse homogenate with 10 μM soman during 18 hr at 0–4° no further binding of the isomers was detected. It is concluded that skin of the three species tested does not contain enzymes that degrade the toxic C(±)P(−)-isomers of soman, whereas phosphorylphosphatase activity for the C(±)P(+)-isomers is present in the skin of all three species. Binding sites for all four soman isomers are only present in mouse skin.