Histochemistry of the Retina: II. Use of Phenazine Methosulfate to Demonstrate the Succinoxidase System

The study of dehydrogenase activity in many tissues, including the retina, has been advanced by the development of biochemical and histochemical methods utilizing tetrazolium salts as electron acceptors.^1-12 Recently, Nachlas, Margulies, and Seligman¹³ have shown that the tetrazolium salts most commonly used accept electrons at different steps in the electron transfer system and not directly from the dehydrogenase. In addition, because the electron transfer occurs through diaphorase, the pattern of tetrazolium precipitation will be dependent upon the localization of diaphorase in the tissue. An attempt was made to exclude the need for diaphorase by adding phenazine methosulfate (PMS), an accessory electron acceptor, to the assay system. This compound was used by Farber and Bueding,⁴ and by Singer, Kearney, and Bernath,¹⁴ and Nachlas, Margulies, and Seligman^9,13 to study the succinoxidase system. Singer et al.¹⁴ demonstrated that PMS accepted electrons directly from reduced succinic dehydrogenase, and