Intra- and extramitochondrial isozymes of (NADP) malate dehydrogenase.

Abstract

The intracellular distribution of (NADP) malate dehydrogenase (decarboxylating) was studied by means of fractional extraction of extra‐ and intramitochondrial enzymes in various tissues of mouse, rat, rabbit, guinea pig, pig, beef, sea gull and pigeon. Absolute activity levels of (NADP) malate dehydrogenase in the same tissues of different species vary greatly. In white adipose tissue and adrenal medulla, (NADP) malate dehydrogenase is located exclusively within the extramitochondrial compartment. In liver, 95% of (NADP) malate dehydrogenase activity is extramitochondrial and only 5% intramitochondrial. Mitochondrial subfractionation reveals a location of this enzyme within the inner mitochondrial compartment. Brain, heart, adrenal cortex and kidney also contain extra‐ and intramitochondrial (NADP) malate dehydrogenase. In kidney and adrenal cortex, the ratio of extra‐ and intramitochondrial isozymes varies between different species. In heart, a relatively constant distribution is found, i. e. 30% of the enzyme activity is extramitochondrial and 70% is intramitochondrial. Extra‐ and intramitochondrial (NADP) malate dehydrogenases show different electrophoretic mobility in all tissues examined and can be characterized as two distinct isoenzymes. Extra‐ and intramitochondrial isozymes of (NADP) malate dehydrogenase are probably related to different metabolic functions in various tissues, e. g. extra‐intramitochondrial hydrogen transfer (malate shuttle) or transhydrogenation reactions.