Influence of some -SH group effectors on the incorporation of mevalonic acid by Pinus pinaster seedlings

Abstract

A study has been made of the action of some -SH group effectors on the incorpo­ ration of mevalonic acid (MVA) by extracts of Pinus pinaster seedlings. Among the protecting substances of thiol groups tested, glutathion has a markedly favourable effect on the phosphorylation of MVA, weak at a concentration of 10”3 M, but espe­ cially strong at IO-2 M. A similar effect, although less marked, is shown by cysteine. Both are sufficiently strong to be able to be followed observing the decrease of ATP at 260 m/x, and the simultaneous appearance of their derivatives.

In the study of some inhibiting substances of -SH groups, the addition of iodoace­ tamide shows that it not only inhibits the production of dimethylalylpyrophosphate by the blocking of the isopentenylpyrophosphate-isomerase activity, but that it acts in the same way on the kinases which catalyse the phosphorylation of MVA, the production of P-MVA and PP-MVA decreasing at the same time. This inhibition is clearly foundat concentrations of 5 X 10“3 M and very strong at 10-2 M. Its effect has been studied with and without glutathion. This compound, at concentrations of 1.66 X 10~3 M, coun­ teracts the inhibiting effect of iodoacetamide at similar concentrations.

p-Hydroxymercuribenzoate completely inhibits the enzyme activity at concentrations of 10~"M. Its effects is weak, but perceptible at 10_sM. The presence of glutathion 1.66 X 10-3 M does not counteract this action when the concentration of the inhibitor is 10-3 M, but does so at a concentration of 10-8M.

The effect of ethylmaleimide is somewhat less than that of p-hydroxymercuriben- zoate at 10-3 M, and it must be pointed out that the inhibition found at IO-2 M is completely counteracted by the addition of glutathion at the same concentration.