Muscle lactic dehydrogenases

The measurement of the activity of rabbit muscle lactic dehydrogenase by integrating the classical initial rate method with an integrated method. 2nd International Conference on Bioinformatics and Biomedical Engineering, iCBBE 2008, pp.1209-1212, ISBN 978-1 244-1748-3, Shanghai, China, May 26-28, 2008... 

E. Racker With purified preparation of glyoxalases we obtained the zinc salt of D-lactic acid which was not oxidized by muscle lactic dehydrogenase. I may add t o this point that synthetic preparation of n, L-lactoyl glutathione which Dr. Wieland has sent us was split to completion by glyoxalase II, which means that both d- and L-lactic acid can be formed and therefore the specificity of the over-all reaction must be due to glyoxalase I. 

Initial reaction velocities were measured at 340 nm. For all experiments (except where noted) the final volume of 1.00 ml of 0.1 M Tris chloride (pH 7.6) contained 13 /ug of rabbit muscle lactic dehydrogenase, 0.05 jug of rabbit muscle pyruvate kinase, 0.1 M KCl, 0.025 M MgS04, 1.5 mM phosphoenolpyruvate (sodium salt), 0.25 mAf ADP (sodium salt), and 0.25 mM NADH. The order of addition of the components was the same as described above for AMP aminohydrolase. 

The copious muscle enzyme efflux in Duchenne-type muscular dystrophy, giving gross serum elevations despite the rapid serum clearance, may well deplete some muscle enzymes that so much aldolase still remains may indicate a replacement so rapid that, if applied to the transaminases and to lactic dehydrogenase, the muscle content may be maintained or even increased, since their serum elevations, though considerable, are proportionately much less than that of aldolase. 

Both are abundant in skeletal muscle, myocardium, liver, and erythrocytes, so that hemolysis must be avoided, and in serum they may be assayed spectrophotometrically by their conversion of phosphate-buffered pyruvate to lactate (R6, W16) or oxalacetate to malate (S25) at the expense of added NADH2, when the rate of decrease of optical density at 340 m x thus measmes the serum activities of the respective enzymes. Recently, however, the reverse reaction has been found best for serum lactic dehydrogenase assay (A2a). In conventional spectrophotometric units the normal ranges are 100-600 units per ml for lactic dehydrogenase (W16) and 42-195 xmits per ml for malic dehydrogenase (S25) as before, one conventional spectrophotometric unit per ml = 0.48 pmoles/ minute/liter (W13). 

Lactic dehydrogenase (LDH) is a tetramer composed of two kinds of subunits called M and H. A large fraction of the skeletal muscle LDH is MMMM. A large fraction of the heart LDH is HHHH. Other tissues contain hybrid isozymes containing both M and H subunits. How many different LDH isozymes are possible Assume that the subunits are arranged in a square or tetrahedral" fashion so that there is no sequence" (i.e., HMMM is the same as MMMH). 

Figure 3 Far-UV circular dichroism spectra of native, denatured, and aggregated forms of LDH-M4 (tetrameric porcine lactic dehydrogenase from skeletal muscle). ( ) native and (O) renatured LDH-M4 at a concentration of 1.5 mg/ml. ( ) LDH-M4 denatured at pH 2 or at ( ) 6 M guanidine hydrochloride, same concentration (A) aggregated LDH-M4 dispersed by low-energy sonication at a concentration of 0.05 mg/ml (determined gravimetrically from the dry weight at 105 C). From Zettlemeissl et al, (75) reproduced with permission.

Lactic dehydrogenase E>ecrease liver, kidney, brain, heart, and skeletal muscle (BID >... 

Isoenzymes (or isozymes) are multiple forms of an enzyme that differ from each other in such properties as substrate affinity, maximum activity, or regulatory properties. They may be found in different tissues or portions of the same cell. For example, thymidine kinase catalyzing phosphorylation occurs as two isoenzymes—one in the cytoplasm and the other associated with the mitochondria of the same mammalian cell. Lactic dehydrogenase, which catalyzes the reduction of pymvic acid to L-lactic acid exists in five isozymic forms. These are tetramers formed by the association of two polypeptides of equal size H (heart) and M (muscle). 

This inhibitor can even discriminate between isoenzymes. Thus, whereas it irreversibly inhibits the lactic dehydrogenase of skeletal muscle, it does not affect that of the heart. A related compound, 5-(phenoxycarbonylamino)salicylic acid, irreverisbly inhibits the heart (but not the skeletal) isoenzyme, whereas its 4-isomer irreversibly inhibits the skeletal (but not the heart) isoenzyme (Baker and Patel, 1964 Baker, 1967). 

In the aorta of normal rabbits fed on stock diet, lactic dehydrogenase, NADH-tetrazolium reductase and adenosine triphosphatase are active in smooth-muscle fibres between elastic lamellae (Adams et al. 1963). Within 4 weeks on a cholesterol-enriched diet, macrophages infiltrate or proliferate in the thickened intima of the aorta and these cells react strongly with the lactic dehydrogenase, NADH-tetrazolium reductase and adenosine triphosphatase methods. 

The lactate produced mainly in muscle diffuses in blood and reaches the heart where the principal function of LDH-H is oxidizing lactate to pyruvate, which can then be utilized through the Krebs cycle. In fact, if blood concentrations of lactate are increased, the uptake of that metabolite by the heart is also increased. Thus, the H-type is the true lactic dehydrogenase, while the M-type is really a pyruvic reductase. 

Pyruvate kinase Lactic dehydrogenase (muscle) Carboxylase 1, , ... 

Lactic Dehydrogenase. Muscle glycolysis is completed by the reduction of pyruvate to L-lactate. The pyridine nucleotide-requiring enzyme. 

Lactic dehydrogenase in yeast differs from the muscle enzyme in the lack of a requirement for, or reaction with, DPN. The yeast enzyme has been purified by Bach, Dixon, and Zerfas and found to be associated with a hemoprotein with reduced bands at 530 and 556 m/x which has been designated as cytochrome b2. The reduced bands appear instantly on addition of lactate, but, as in the case of heart muscle succinic dehydrogenase, the identity of the hemoprotein with lactic dehydrogenase has not been fully established. Crude preparations will reduce cytochrome c, but this activity is diminished on purification. An additional factor is thought to be required for the reaction with cytochrome c. The reduced cytochrome b2 is slowly reoxidized by air. 

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