Abstract
Succinyl lecithin has been used as substrate in the histochemical succinate-tetrazolium reductase system; it is as acceptable to the tissue system as is succinate. Cholesterol succinate, however, is not utilized by this system. It is inferred that the amphophilic nature of succinyl lecithin allows this substrate to penetrate lipid-rich mitochondrial membranes, whereas cholesterol succinate's more hydrophobic nature impedes its movement at such lipid-water interfaces. It must be emphasized that this study does not reveal whether or not succinyl lecithin is a physiologic substrate.