Abstract
This cytochemical study of differentiating prosobranch spermatids demonstrates changes in the localization of intramitochondrial cytochrome c oxidase activity during the course of mitochondrial fusion and internal reorganization. Using the osmiophilic compound 3,3'-diaminobenzidine, activity for cytochrome c oxidase is localized in or on the internal mitochondrial membranes and within the intracristal compartment of metamorphosing mitochondria. However, some enzyme activity consistently appears in the matrix. Enzyme reaction product in the matrix disappears as the internal membranes become organized, and in mature spermatozoa activity for cytochrome c oxidase appears only on cristae and in the intracristal space. It is hypothesized that positive matrix material could either represent enzyme molecules not yet incorporated into membranes or disaggregated products of membrane breakdown associated with remodeling of the cristae.