Detection of an NAD(+)-dependent malic enzyme locus in the Atlantic salmon Salmo salar and other salmonid fish.

Electrophoretic studies of malate oxidoreductases routinely assess variation in two enzymes, malate dehydrogenase (EC 1.1.1.37) and malic enzyme (NADP+) (EC 1.1.1.40). By modification of the standard isozyme staining conditions for these enzymes, we have resolved a new NAD(+)-preferring, MgCl2-requiring malic enzyme which is indicated to be EC 1.1.1.39. The enzyme was detected in 10 salmonid fish species of the genera Salmo, Salvelinus, and Onchorynchus. Phenotypic variation indicates that the novel enzyme is tetrameric and coded by a single locus. Inheritance in S. salar follows a single-locus model and the phenotypes are unlinked to polymorphisms for sMDH-3,4* and mMEP-2*, two malate oxidoreductase loci previously shown to be variable in this species.