About 80% of the aminoacid sequence of dogfish (Squalus acanthius) M(4) lactate dehydrogenase (EC 1.1.1.27) has been elucidated. Several sequence homologies with peptides from pig H(4) and pig M(4) lactate dehydrogenase are identified. Histidine 195 is homologous to the essential histidine residue in pig H(4) lactate dehydrogenase. Similarities in the sequence around the "essential" cysteine residue of lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and yeast and liver alcohol dehydrogenase are delineated.

Amino Acid Sequence↗

PubMed1973

Structure-function relationships in lactate dehydrogenase.

The binding of coenzyme and substrate are considered in relation to the known primary and tertiary structure of lactate dehydrogenase (EC 1.1.1.27). The adenine binds in a hydrophobic crevice, and the two coenzyme phosphates are oriented by interactions with the protein. The positively charged guanidinium group of arginine 101 then folds over the negatively charged phosphates, collapsing the loop region over the active center and positioning the unreactive B side of the nicotinamide in a hydrophobic protein environment. Collapse of the loop also introduces various charged groups into the vicinity of the substrate binding site. The substrate is situated between histidine 195 and the C4 position on the nicotinamide ring, and is partially oriented by interactions between its carboxyl group and arginine 171. The spatial arrangements of these groups may provide the specificity for the L-isomer of lactate.

Amino Acid Sequence↗

PubMed1972

An adenosine triphosphate-phosphate exchange catalyzed by a soluble enzyme couple inhibited by uncouplers of oxidative phosphorylation.

The sulfenic acid form of glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12), which is an acyl phosphatase, will catalyze an acetyl phosphate-Pi exchange reaction. This exchange reaction is reversibly inhibited by the uncouplers of oxidative phosphorylation, 2,4-dinitrophenol, m-Cl carbonylcyanide-phenylhydrazone, pentachlorophenol, and 5-chloro-3-tert-butyl-2'-chloro-4'-nitrosalicylanalide, and is irreversibly inhibited by cyanide and dicumarol. An ATP-Pi exchange reaction similar to that catalyzed by mitochondria can be simulated by a system composed of oxidized glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase (EC 2.7.1.28), 3-phosphoglycerate, ATP, (32)Pi, and appropriate cofactors. The ATP-Pi exchange is inhibited by uncouplers of oxidative phosphorylation. Higher concentrations of uncouplers will also inhibit the ATPase reaction catalyzed by the coupled enzyme system. The exchange reactions catalyzed by the sulfenic acid form of glyceraldehyde-3-phosphate are consistent with a sulfenyl carboxylate intermediate. On the basis of these observations, a reaction scheme has been postulated for covalent coupling in oxidative phosphorylation that includes a sulfenyl carboxylate as a nonphosphorylated, high energy intermediate and an acyl phosphate as a phosphorylated, high energy intermediate.

Adenosine Triphosphate↗

PubMed1971