Amino acid malate dehydrogenase composition

Not unexpectedly, there is a marked similarity in the composition of the mitochondrial and supernatant isozymes when compared with the same isozyme from other species, although in the latter case, the two salmon enzymes, which appear to be genetic variants, differ somewhat more than do the malate dehydrogenases from pig, beef, and chicken sources. As noted previously 40), there is also quite a pronounced similarity between the profiles presented by the two cellular isozymes. The most notable difference in the amino acid composition is the absence of tryptophan in mitochondrial malate dehydrogenase. 

Amino Acid Composition op the Cytoplasmic and Mitochondrial Malate Dehydrogenases... 

Mitochondrial malate dehydrogenase (MDH) from several species has been shown to exist in several enzymically active forms which also appear to be conformational isoenzymes (Kitto et al, 1966, 1970). Kitto et al (1970) showed, in contrast to Epstein and Schechter (1968), that these MDH s were interconvertible in vitro, had the same amino acid compositions and molecular weights, but differed, once reversibly denatured, considerably in their heat stability. Similar interconversion of isoenzymes has also been observed with purified preparations of horse liver alcohol dehydrogenase (Lutstorf and von Wartburg, 1969). The question arises if such conformers are of any physiological or functional significance. It is possible that beeause of their differences in surface charge, the various conformative isoenzymes are differently bound within a cell. 

N. crassa m-, and E. coli. In each case, identical elution positions were observed corresponding to a molecular weight of 67,000. This study eliminates the possibility that the mitochondrial and cytoplasmic isozymes vary markedly in size. In addition. X-ray diffraction studies (57) and amino acid sequence analysis (55) have clearly established that the cytoplasmic form of pig heart malate dehydrogenase to be about 72,000. Sequence (55) and compositional analyses i/fi) of the mitochondrial en-... 

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