Biomaterial Database

Influence of salts on Michaelis-constant values for NADH. 1977

B F Howell, and S McCune, and R Schaffer

We previously observed [Clin. Chem. 22, 1648 (1976)] that values of the Michaelis constant for NADH for the conversion of pyruvate to lactate with lactate dehydrogenase (EC 1.1.1.27) in the presence of 0.1 mol/liter buffers at 25 degrees C showed first-order dependence on enzyme concentration. This is now recognized to be the result of an inhibitory influence exerted by buffers [NH4HCO2, tris(hydroxymethyl)aminomethane, and phosphate] and salts [(NH4)2SO4 and NaCl] present in the reaction mixtures. Inhibition constants for the enzyme/inhibitor complexes formed with these substances are about 0.3 mol/liter for competition of NH4HCO3 with NaOH and 0.4 mol/liter for competition of NH4HCO3 with pyruvate; they are 0.6 mol/liter for NaCl, 1.0 mol/liter for sodium phosphate, 0.3 mol/liter for (NH4)2SO4, and 0.8 mol/liter for tris(hydroxymethyl)aminomethane when these substances compete with NADH. Because of the large molar ratio of buffer to substrate (about 10(9):1) in enzymatic assays, the buffer concentration significantly influences the Michaelis constant, despite the large value for the inhibition constant. Attention to the concentrations of these substances may be required for decreasing variability in clinical assays in which lactate dehydrogenase and possible other enzymes are used.

UI	MeSH Term	Description	Entries
D007527	Isoenzymes	Structurally related forms of an enzyme. Each isoenzyme has the same mechanism and classification, but differs in its chemical, physical, or immunological characteristics.	Alloenzyme,Allozyme,Isoenzyme,Isozyme,Isozymes,Alloenzymes,Allozymes
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D007770	L-Lactate Dehydrogenase	A tetrameric enzyme that, along with the coenzyme NAD+, catalyzes the interconversion of LACTATE and PYRUVATE. In vertebrates, genes for three different subunits (LDH-A, LDH-B and LDH-C) exist.	Lactate Dehydrogenase,Dehydrogenase, L-Lactate,Dehydrogenase, Lactate,L Lactate Dehydrogenase
D008433	Mathematics	The deductive study of shape, quantity, and dependence. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)	Mathematic
D009243	NAD	A coenzyme composed of ribosylnicotinamide 5'-diphosphate coupled to adenosine 5'-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH). (Dorland, 27th ed)	Coenzyme I,DPN,Diphosphopyridine Nucleotide,Nadide,Nicotinamide-Adenine Dinucleotide,Dihydronicotinamide Adenine Dinucleotide,NADH,Adenine Dinucleotide, Dihydronicotinamide,Dinucleotide, Dihydronicotinamide Adenine,Dinucleotide, Nicotinamide-Adenine,Nicotinamide Adenine Dinucleotide,Nucleotide, Diphosphopyridine
D010084	Oxidation-Reduction	A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).	Redox,Oxidation Reduction
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013552	Swine	Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).	Phacochoerus,Pigs,Suidae,Warthogs,Wart Hogs,Hog, Wart,Hogs, Wart,Wart Hog