Abstract
1. The non-enzymatic reduction of tetrazolium salts by SH groups was studied mainly in the keratogenous zone of the hair.
2. The effect of non-enzymatic reduction of tetrazolium salts by SH groups is pH-dependent, beginning at about pH4.4, gradually increasing up to pH7.0 and continuing to increase rapidly thereafter until pH13 which is the highest alkaline pH tested. Addition of diphosphopyridine nucleotide (DPN) intensifies the reaction.
3. It was shown that several inorganic as well as organic substance having SH groups can reduce tetrazolium salts in vitro.
4. It is concluded that the hydrogen of SH groups can be transferred directly to tetrazolium salts in addition to the pathway via specific diaphorases as described by ZIMMERMAN and PEARSE (1959). The main implication of this fact is that the precise histochemical localization of not only coenzyme-linked dehydrogenases but also cytochrome-linked dehydrogenases may be difficult without proper controls for tissue-SH.
5. Since it was found that sodium cyanide higher than 0.01M in the final concentration of the incubation medium can also reduce tetrazolium salts, which may result in the false positive localization of enzymes, the concentration of the sodium cyanide should be kept lower than 0.01M in the incubation medium in the histochemical demonstration of coenzyme-linked dehydrogenases.
