The topography of porcine lactate dehydrogenase isoenzyme H4. The identification of lysines on the surface.

Porcine lactate dehydrogenase isoenzyme H4 was treated with methyl 6-(2,4-dinitrophenylamino)hexanimidate hydrochloride and the lysines modified hereby were identified. For this purpose 20 chymotryptic-tryptic N epsilon-[6-(2,4-dinitrophenylamino)hexanimidoyl]lysine containing peptides were isolated by means of gel chromatography, countercurrent distribution, thin-layer chromatography and ion-exchange chromatography. Their amino acid composition, the amino end groups and their electrophoretic mobilities were determined. With these data, the known primary structure of the procine lactate dehydrogenase isoenzyme H4 and the 6-A resolution structure analysis performed by Rossmann et al.[1] we identified the following lysines on the surface of the quarternary structure of the enzyme: no. 4, 6, 60, 77, 82, 121, 157, 179, 226, 230, 241, 306, 308, 316, 327 and 330. No modified lysine peptides were found in the intersubunit binding sites.