C. Interaction of Maleic Acid with Thiol Compounds

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. Titration experiments The following solutions were prepared: (1) a 0-2M solution of the Na salt of the unsaturated acid (A); (2) a solution of the Na salt of the thiol compound such that 1 ml. was equivalent to 40 ml. 0-01N iodine, i.e. 0-4M with respect to SH (B). For experiment x ml. of A and y ml. of B were placed in each of a series of Thunberg tubes together with S0rensen's phosphate buffer, pH 7-4 (1 ml. for every 4 ml. final volume) and water to the required volume. The tubes were evacuated and incubated at 37°.