ACETYL DISULFIDE, (CH3COS)2, A MAJOR ACTIVE COMPONENT IN THE THIOLACETIC ACID HISTOCHEMICAL METHOD FOR ACETYLCHOLINESTERASE

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Abstract
Triple distilled thiolacetic acid (TA) was found to be much less active as a histochemical substrate for acetylcholinesterase (AChE) of mouse intercostal muscle than either the original, impure preparation, thiolacetic acid (practical, Eastman) or the residue from the first distillation. Iodimetric titration showed that the crude preparation had only 92-94% of its theoretical TA content, which fell to 70-72% with storage. Findings from column and thin layer chromatography and ether-water extraction indicated that the active material is relatively polar and acidic, and contains an S—S group. The addition of 0.0015-0.006 M acetyl disulfide (AcDiS) to 0.03 M triple distilled TA markedly enhanced the substrate activity of the latter so that it matched that of 0.03 M thiolacetic acid (practical); treatment with the reducing agents, sodium ascorbate and sodium borohydride, reduced the substrate activity of both the mixtures and thiolacetic acid (practical) but not that of triple distilled TA alone. Mass spectrometric examination of thiolacetic acid (practical), the distillation residue and a benzene extract of extemporaneously prepared AcDiS showed the presence in each of a peak at mass 150 (the molecular weight of AcDiS), which was not present in triple distilled TA. All except the AcDiS extract showed a peak also at mass 76 (the molecular weight of TA). It was concluded that AcDiS is the major component of thiolacetic acid (practical) that is responsible for its enhanced activity as a histochemical substrate for AChE.

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