Association of the Testicular Lactate Dehydrogenase Isozyme with a Special Type of Mitochondria1

Abstract

Subfractions from adult rat testis mitochondria have been separated by a sucrose-density gradient and lactate dehydrogenase activity and isozyme content of each subfraction were determined. Studies by electron microscopy revealed that the subfraction in which the additional isozymes (LDH-X) are contained is composed predominantly of a peculiar type of mitochondria. These mitochondria, showing an atypical internal configuration, appear initially in primary spermatocytes, increase in number in subsequent stages of gametogenesis, and are the only mitochondrial species present in spermatids and spermatozoa. Results suggest that these organelles are the unique cellular site in which LDH-X is located.