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Amino- and Carboxyl-terminal Analyses of Hepatoma Lactate Dehydrogenase Isozymes¹

Departments of Pediatrics and Biochemistry, The University of Iowa College of Medicine, Iowa City, Iowa 52242

The M₄ isozyme of lactate dehydrogenase was purified to homogeneity from normal rat liver and from two Morris hepatomas (7777 and 7793). Amino-terminal analyses with fluorodinitrobenzene failed to detect the presence of free amino-terminal residues in each enzyme studied. Each enzyme contained between 3.7 and 4.1 moles of protein-bound acetyl groups per mole of enzyme. The amino-terminal peptide, characterized as N-acetylalanylalanine, was isolated from Pronase digests of each isozyme preparation, and quantitative recovery experiments indicated that all acetyl residues were bound at the amino termini. Carboxyl-terminal analyses demonstrated phenylalanine to be the carboxyl-terminal residue in each enzyme studied. These data indicate no differences in either amino- or carboxyl-terminal regions of the hepatoma M₄ isozymes compared to normal liver M₄ isozyme.

¹ This research was supported in part by Grants AM 15857, CA 10729, an CA 07617 from the NIH.

² To whom reprint requests should be addressed.

Received 10/16/74. Accepted 2/11/75.