Succinic dehydrogenase activity in the epidermis of Natrix piscator during its sloughing cycle

Succinic dehydrogenase activity, in the epidermis of Nairix piscutor in different stages of sloughing cycle, has been localized using a nitro‐BT technique with appropriate controls. The staining properties of different layers in scale epidermis are similar to the corresponding layers in hinge epidermis. In the stratum germinativum, the layers of undifferentiated epidermal cells in all stages of the sloughing cycle, and in the lacunar tissue of Stages 3,4 and 5, a positive though weak reaction for SDH activity reflects the active metabolic state of the cells in these layers. Loss of SDH activity in Stage 6 indicates an inactive metabolic state of the lacunar tissue cells, corresponding with their disintegration owing to the cessation of nutrients as a result of keratinization of cells in the underlying layers. The Oberhautchen, mesos and alpha layers in all Stages, and the clear layer cells in Stages 5 and 6 (outer epidermal generation), the presumptive Oberhautchen, presumptive mesos layer and presumptive alpha layer in all stages of their differentiation, and the presumptive beta layer in Stages 3 and 4 (inner epidermal generation) all stain purple with nitro‐BT technique even in sections incubated in the medium without the substrate‐succinate. The reaction is inhibited by prior treatment with 0.1 M N‐ethyl maleimide blocking protein‐bound ‐SH groups. This suggests that the reaction is due to the presence of protein‐bound ‐SH groups in these sites. The reduced intensity of reaction in the mature beta layer of the outer epidermal generation, and in the presumptive beta layer in Stages 5 and 6 of the inner epidermal generation, is due to simultaneous loss of their content of ‐SH groups with maturation and keratinization.