Glycine synthase complex

Glycine. The glycine synthase complex of Ever mitochondria sphts glycine to COj and NH4+ and forms A, A -methylene tetrahydrofolate (Figure 30-5). 

Figure 30-6. Reversible cleavage of glycine by the mitochondrial glycine synthase complex. (PLP, pyri-doxal phosphate.)...

The one-carbon carrier N, N -methylenetetrahydrofolate is derived from reactions of the one-carbon pool (Chapter 27). [The term one-carbon pool refers to all single-carbon-containing metabolites (e.g., -CH3, -CHO, NH=C-, etc.) that can be utilized in biosynthetic reactions such as formation of purine and pyrimidine.] These reactions include oxidation of glycine by glycine cleavage enzyme complex (glycine synthase) ... 

Threonine can be broken down by two separate pathways. Serine dehydratase catalyzes the conversion of threonine to 2-ketobut ate plus an ammonium ion 2-ketobutyrate is then converted by branched-chain keto add (BCKA) dehydrogenase to propionyl-CoA plus carbon dioxide. Propionyl-CoA catabolism is described later in this chapter. Threonine can also be broken down by a complex that has been suggested to be composed of threonine dehydrogenase and acetoacetone synthase (Tressel et ah, 1986). Here, threonine catabolism results in the production of acetyl-CoA plus glycine. 

The B. subtilis thiazole synthase (ThiG) catalyzes the condensation of DXP (2), glycine imine (23), and ThiS-COSH (3) to give the thiazole tautomer 14. The current mechanistic hypothesis for this complex reaction is shown in Figure 5. DXP forms an imine with lysine 96, which then tautomerizes to ketone 17. Addition of ThiS-COSH... 

A more complex case was described % Nandi (1978). -Aminolevulinic acid synthase from Rhodopseudomonas spheroides is a pyridoxal phosphate-dependent enzyme that catalyzes the formation of -aminolevulinic acid from glycine and succinyl coenzyme A in this case, the release of products is random and more than one product can exchange back into substrate. 

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