The results obtained by us (1948a) with maleic acid as an inhibitor of mitosis have been developed in an attempt to prepare other mitotic inhibitors related to maleic acid; in particular we have investigated the antimitotic activity of substances in which the maleic acid residue is part of an aliphatic ring. The imides of maleic acid (I) and of citraconic acid (II), N-ethylmaleimide (III), -and in addition succinimide (IV) were chosen for this purpose.

IT was observed by one of us (E. J. M.) that the titratable SH of glutathione was greatly decreased by incubation with maleic acid in absence or in presence of oxygen at pH 7x4 and 370 (but not with fumaric acid). Thiolacetic acid and cysteine behaved similarly to glutathione. The results contained in this paper show that the disappearance of the SH-groups is due to the circumstance that each of the three substances studied yields an addition compound with maleic acid in the formation of which these groups are involved. The kinetics of such reactions show points of special interest.

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