Distribution of lactate dehydrogenase isozymes in subcellular fractions of rat tissues

Subcellular fractions from adult rat testis and kidney have been investigated for their lactate dehydrogenase isozymes content. A fraction from testis homogenates, showing predominance of mitochondria with dense matrix and dilated cristae, was revealed to contain most of the additional isozymes (“X”) specific of testis and sperm. These molecular forms showed a high degree of compartmentation. A small proportion of total lactate dehydrogenase activity in kidney is associated with the microsomal fraction. That portion is entirely represented by isozyme 5, a molecular species usually not detected in whole kidney homogenates. Patterns of elution of the bound enzyme with different salt concentrations and detergents indicated that the forces involved in that association must be complex and that they possibly can operate in vivo.