Subcellular distribution of the lactate dehydrogenase isozyme specific for testis and sperm

Lactate dehydrogenase isozyme X (LDH X) was determined in subfractions of mouse testis homogenates using 2-oxoglutarate and 2-oxoisocaproate as substrates. LDH X is associated with a special type of mitochondria found in cells of the spermatogenic line and in the mitochondrial sheath of spermatozoa, and it is also distributed in the cytoplasmic soluble phase. Intramitochondrial localization of LDH X was studied by separating the organelle membranes with two different methods (digitonin and swelling-shrinking treatments). The results indicate that the isozyme X is located in the matrix.