A reappraisal of some structural features of bovine heart malate dehydrogenase.

1. Malate dehydrogenase of the mitochondrial type was prepared from an acetone-prepared powder of thoroughly washed minces of whole bovine heart by previously reported methods that were modified to give higher yields of the purified enzyme. 2. Determinations of the sedimentation and diffusion coefficients showed the molecular weight of the enzyme to be approx. 63000. The amino acid composition of the enzyme was also determined. Discrepancies between these data and similar data previously reported by Davies & Kun (1957) and Siegel & Englard (1962) were resolved. 3. ;Fingerprints' were made from tryptic digests of heat-denatured and of reduced and alkylated enzyme. These indicated that the enzyme is composed of a number of identical or similar sub-units.