Yeast glutamate dehydrogenases

Figure 2. SDS gel electrophoresis of the products of partial cystine cleavage for several test proteins. A. molecular weight standards, B. yeast alcohol dehydrogenase. C. P-lactoglobulin, D. hen egg lysozyme, E. ovalbumin, F. calf fetal serum fetuin. Molecular weight standards are indicated by arrows on the left side of the gel and are bovine serum albumin (66,300), bovine liver glutamate dehydrogenase (55,400), porcine muscle lactate ddiydiogenase (36,500), bovine erythrocyte carbonic anhydrase (31,000), soybean trypsin inhibitor (21,500), hen egg lysozyme (14,400), bovine lung aprotinin (6,000), unresolved bovine pancreatic insulin A and B chains.

Most commonly, alcohol dehydrogenase (E.C. 1.1.1.1) from yeast (YADH), horse liver (HLADH), or Thermoanaerobium hrockii (TBADH) as well as glutamate dehydrogenase (E.C. 1.4.1.2.) or lactate dehydrogenase (E.C. 1.1.1.27) are used for NAD(P)+ regeneration (Table 16.2-1). Thus, the reduction equivalents are transferred to an aldehyde or ketone as terminal electron acceptor yielding the corresponding alcohols. 

Drillien, R., Aigle, M., and Lacroute, F. (1973). Yeast mutants pleiotropically impaired in the regulation of the two glutamate dehydrogenases. Biochem. Biophys. Res. Commun. 53, 367-372. 

Glutamic dehydrogenase has been detected in bacteria, yeast, plants, and animal tissues. The enzyme has been purified extensively only from liver, and the properties of the ezyme from other sources are not known very precisely. It has been reported that glutamic dehydrogenase of plants requires DPN, while the enzyme of yeast and E. coli requires TPN. The mammalian enzyme uses both coenzymes. 

We have emphasized the specific character of macromolecules. Even in the arsenal of enzymes common to all cells we find indications of this specificity. The glucose dehydrogenase of vertebrate liver for example, is not inhibited by toluene, whilst that of E. colt is inhibited. Yeast alcohol dehydrogenase is completely inhibited by O-OOIM iodoacetate, whilst even at a concentration of O-OIM, animal alcohol dehydrogenase remains imaffected. Glutamic add dehydrogenase of yeast requires TPN as a coenzyme whilst the same enzyme from plants needs DPN. 

In yeast grown under hypoxic conditions succinate accumulates and the Krebs cycle is split in two branches, one diverging from oxaloacetate to succinate with simultaneous NAD recovery and the other one from oxaloacetate to glutamate, in which the NADP-linked isocitrate dehydrogenase produces the substrates needed for the NADP-linked glutamate dehydrogenase, namely 2-oxoglutarate and NADPH.< )... 

Physiological substrates, however, such as apotryptophan synthase, cytoplasmic malate dehydrogenase or NAD-dependent glutamate dehydrogenase from yeast, are attacked by proteinase A at neutral pH (4,7). Results from experiments on the sensitivity of hemoglobin and yeast-apotryptophan synthase, respectively, to yeast proteinase A are shown in Figure 2. 

In 1980, Miflin and Lea pointed out that much of the information on biochemical pathways has arisen from the use of mutants of bacteria and yeast larking key enzymes. They complained at the time that no mutants of higher plants were available in the ammonia assimilation pathway. A glance at Table I clearly indicates that a number of such mutants are now available. In addition mutants of maize with low (but not zero) levels of glutamate dehydrogenase have also been studied (Rhodes et ai, 1989). 

This mechanism is supported by the fact that every 3-oxoalkylarsonic acid studied also eliminated arsenite. First, 3-hyroxypropylarsonic acid proved to be a substrate for alcohol dehydrogenase from yeast, and similarly eliminated arsenite. Further, the oxidation by periodate of the HO—CH2—CHOH—CH2—CH2—As03H2, expected to produce 0=CH—CH2—CH2—As03H2 (another 3-oxoalkylarsonic acid), also yielded arsenite, and conditions that normally transaminate amino acids, when applied to the glutamate analogue HOOC—CH(—NH2)—... 

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