Anaerobic transamination reaction

Love and coworkers have reported a series of dinuclear cobalt complexes derived from a rigid binucleating macrocycle H4L 18 as shown in Fig. 26 (150). The synthesis of the dicobalt complex [Co2(L18)] (36) was achieved by an anaerobic transamination reaction between H4L18 and [Co(thf) N(SiMe3)2 2] in THF. The unsaturated species 36 forms a bis(pyridine) adduct, 36 py2 (py — pyridine), which has a cleft-like structure reminiscent of pacman diporphyrin complexes (151,152). Both cobalt ions are square pyramidal, with Col and Co2 displaced out of the N4-basal planes by 0.17 and 0.18 A, respectively. The apical sites are occupied by pyridine nitrogen atoms that are exo and endo to the cleft. Interestingly the endo pyridine is canted and reflects the... 

The glucose-alanine cycle. Active muscle functions anaerobically and synthesizes alanine by a transamination reaction between glutamate and pyruvate, The alanine is transported to the liver, where the... 

GDH from the anaerobe Clostridium SB4 is NAD specific the enzyme is probably responsible for the production of a-ketoglutarate, required as a substrate for transamination reactions and for the citric acid cycle... 

In 1937, Alexander E. Braunstein (1902-86), working in Moscow, was studying the metabolism of glutamate in muscles and made the interesting observation that when glutamate levels decrease so do lactate (anaerobic conditions) or pyruvate (aerobic conditions). In each case the concentrations of alanine increase. He had discovered the reversible transamination reactions that connect the intermediary metabolisms of proteins and carbohydrates. 

E. coli (107, 125). The complexes have recently been reviewed (126). It is possible that lipoamide dehydrogenase also functions in the complexes that oxidatively decarboxylate the a-keto acids resulting from the transamination of valine, isoleucine, and leucine but these have proved difficult to resolve (127). Lipoamide dehydrogenase also functions in the pyridoxal phosphate and tetrahydrofolate-dependent oxidative decarboxylation of glycine in the anaerobic bacterium Peptococcus glyci-nophilus. The reaction in which the protein-bound lipoic acid is reduced is very complex and not yet fully understood the ultimate electron acceptor is NAD+ (112,113,128). 

Studies of the carbohydrate metabolism of T. cruzi (21) have shown that phos-phoenolpyruvate serves as the acceptor of the primary COj-fixation reaction. This resulted in the formation of oxaloacetate and malate and the excretion of succinate. The central role of PEPCK in energy metabolism in insect-stage trypanosomatids has been illustrated in the case of T. cruzi epimastigotes, using 3-mercaptopicolinic aeid, a powerful inhibitor of this enzyme (22). Inhibition led to a twofold reduction in the anaerobic production of succinate and a similar decrease in glucose consumption, while the production of alanine, via the transamination of pyruvate, increased threefold. 

The reaction is markedly accelerated by the addition of ammonia leads to the formation of the N Mabeled amino acid and spectrophoto-metric studies show that the reduced amino acid oxidase can be reoxidized anaerobically by the addition of ammonia and a-keto acid. All oi these experiments indicate that the reaction observed does not involve a transamination. It has been suggested that imder appropriate phyinological conditions a reversal of the amino acid oxidase reaction may be responsible for amino acid synthesis. 

There are apparently two distinct enzymic reactions which result in the anaerobic degradation of cysteine. The first is a direct desfilfhydration, the second is initiated by transamination with a-ketoglutarate to yield glutamate and 8-mercaptopyruvate. According to the original observations of Desnuelle and Fromageot, Smythe and others (71) the mechanism of cysteine desulfhydrase action is as follows ... 

Phenylacetic acid is another compound which has served as a precursor of tropic acid. Good incorporations (compared with phenylalanine) of [l- C]phenylacetic acid into tropic acid have been reported. Degradations carried out on this tropic acid were consistent with all the activity being located at C-3. In view of the work with the doubly labelled phenylalanine, it is unlikely that phenylacetic acid is an intermediate between phenylalanine and tropic acid. The incorporation of phenylacetic acid can be rationalized if it is assumed that it undergoes a carboxylation leading to phenylpynivic acid and thence to phenylalanine by transamination. This reaction has been observed by Allison in ruminal bacteria and photosynthetic anaerobic bacteria. He showed that phenylalanine derived from [I- C]phenylacetic was labelled solely at C-2. ... 

---