A Fourth Malate Dehydrogenase (MDH) Locus in Cucumber

A new malate dehydrogenase (MDH) locus ( Mdh ) was identified in cucumber ( Cucumis sativus L.) by using an extraction buffer containing sucrose and 2-mercaptoethanol. This fourth locus localizes on starch gels between the previously described Mdh -2 and Mdh -3 loci, necessitating the renaming of existing loci. Given previous MDH nomenclature in cucumber, this locus should be Mdh-3 , and the former Mdh-3 is more correctly labeled Mdh-4 . Mdh-x designates the interlocus heteromer formed between Mdh-2 and Mdh-4 . Interpreting our data in terms of previous work, we hypothesize that Mdh-1 codes for a microbody isozyme; Mdh-2 , Mdh-4 , and Mdh-x code for cytosolic isozymes; and Mdh-3 codes for a mitochondrial isozyme.