Triosephosphate dehydrogenase

A period in the United States in 1939 as a Rockefeller Fellow in the Harvard laboratory of E. J. Cohn widened his experience of proteins and knowledge of their physical chemistry and led to his first crystallization of a muscle jirotein, a myogen from rabbit muscle which was later shown hy other workers to be identical with triosephosphate dehydrogenase. 

NAD-dependent glyceraldehyde-3-phosphate dehydrogenase. Triosephosphate dehydrogenase. GAPDH. 

Zinc may be involved in the biosynthesis of tryptophan, a precursor of indole-3-acetic acid (lAA) (51). Zinc also participates in the metabolism of the plant as an activator of several enzymes. Zinc may act as an activator for some phosphate transferring enzymes such as hexose kinase or triosephosphate dehydrogenase. Zinc deficiency results in the accumulation of soluble nitrogen compunds such as amides and amino acids (52). Apparently zinc plays an important role in protein synthesis. 

TABLE 1. The distribution of marker enzyme activites in fractions obtained from pine protoplasts by differential centrifugation. The total activites (pmol (mg chi) h l) was 22 for PEPcarboxylase (PEPcase), 32 for fiimarase, and 69 for NADP triosephosphate dehydrogenase (NADP-TPD), respectively. The values are the means frcxn two separate fraction experiments. 

A more complex example, triosephosphate dehydrogenase, is strongly inhibited by a tetrose bisphosphate that contaminates preparations of glycolaldehyde phosphate, of which it is a condensation product. The... 

In the course of reactions 1 to-4, a molecule of glucose has been transformed into a mixture of F—1,6—PP and two triosephosphates. Now occurs the first anaerobic oxido-reduction (see p. 142) in which, in the presence of triosephosphate dehydrogenase and its coenzyme DPN, an internal oxido-reduction takes place forming 1,3-diphosphoglyceric acid, a molecule containing an energy-rich acylphosphate bond. 

The cycle contains two oxidations, each coupled with TPN (and not DPN which in general is the coenzyme required in glycolysis). Glycolysis is inhibited by fluoride and iodoacetate or bromacetate, the first affecting enolase and the second triosephosphate-dehydrogenase. 

Many protein systems betides those discussed have been subjected to oxidative studies. Some of these are carbonic anbydrase (52), papain, and catheptic-like enzymes (53-57), invertase (58), succinic dehydrogenase (59), triosephosphate dehydrogenase (60), glycerol oxidase (61), and scarlet fever toxin (62). 

Strict specificity toward a coenzyme regardless of the source material. Alcohol dehydrogenase isolated from yeast and horse liver reacts with DPN but not at all with TPN. Triosephosphate dehydrogenase might have been cited as another example of strict DPN specificity except that current... 

There are four enzymes in the glycolytic system which have more than usual interest from the standpoint of this chapter viz., triosephosphate dehydrogenase (T.D.), enolase, aldolase, and phos-phoglucoisomerase. The interaction of T.D. with its substrate (3-p-triose), DPN, and Pi may be represented as follows ... 

The triosephosphate dehydrogenase carries out a reaction similar to the kinase reaction catalyzed by heteroatom mutases. The product of... 

Triosephosphate dehydrogenase —oxidation of triosephosphate to phosphoglyceryl-S, phosphorolysis of phosphoglyceryl-S to diphospho-glycerate, where S is the sulfur of some suhhydryl group in the enzyme. 

It has been known for sometime that in the oxidation of phospho-glyceraldehyde to phosphoglyceric acid, ADP is required. Closer inspection indicated that two independent enzyme systems are involved, one being triosephosphate dehydrogenase which catalyzes the formation of 1,3-diphosphoglyceric acid, and the other a specific enzyme responsible for the transfer of the phosphate of 1,3-diphosphoglyceric acid to ADP. Adenylic acid is inert except in the presence of adenylic kinase. 

The crystalline protein shows a significant absorption band at 260-mju, suggesting that this dehydrogenase may contain bound DPN similarly to muscle triosephosphate dehydrogenase. 

The second type of a-glycerolphosphate dehydrogenase was first described by Green" as a particulate system which was coupled to cytochrome c. This particulate system has now been solubilized by treatment with sodium desoxycholate. On further purification the enzyme was separated from triosephosphate dehydrogenase, isomerase, and catalase activities and no longer was capable of reducing cytochrome c. It also did not react with DPN, TPN, or FAD, although it readily reduced suitable dyes. The reaction product was dihydroxyacetone phosphate. 

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