Glycine heme labeling with

The route to ALA is called, naturally enough, the Shemin route. ALA is a much better precursor of heme than glycine. This was shown by making ALA labelled with both and radioactive C. Incubating this labelled ALA with the enzymes responsible for heme metabolism showed that all the and ended up in the heme. 

After it had been shown in chick embryo liver culture treated with inhibitors that RNA and protein synthesis were required for induction of ALA-synthetase [24,25], these results were confirmed in whole-animal studies [77-79]. Narisawa and Kikuchi [79] were able to detect an increase of ALA-synthetase in the liver 1 to 2 hours after a single subcutaneous dose of 400 mg of ALA per kilogram. It was also shown that not only porphyrins but heme synthesis was increased in chemical porphyria. DeMatteis and Rimington [80], using 2- " C-glycine or Fe, found an increased heme labeling in the presence of the inducers sedormid, AIA, and griseofulvin. It was not determined whether total heme was increased or whether heme turnover had increased. 

This highly distinctive labeling pattern led Shemin to propose that a heme precursor is formed by the condensation of glycine with an activated succinyl compound. In fact, the first step in the biosynthesis ofporphyrins in mammals is the condensation of glycine and succinyl CoA to form 8-aminolevulinate. 

The need for C-labeled analogues of DALA for the elucidation of biosynthetic and metabolic pathways towards heme and chlorophyll in living cells led to the development of other synthetic routes. The reaction of succinoyl chloride monoesters with C-labeled potassium cyanide provided a straightforward route towards acyl cyanides that are convenient precursors for DALA (24-27). More recently, a versatile and efficient syntheses of C-4-, C-5- and N-DALA was reported (28). The pathway for these syntheses was based on a chain elongation of isotopically labeled glycines. 

The now classic labeling experiments of Shemin, Rittenberg, and co-workers [39] with glycine, acetate, and succinate led to the recognition that ALA was the first product of the biosynthetic chain of heme. ALA is formed from glycine and succinyl-CoA according to reaction (1). 

Fig. 19. N concentration in heme and stercobilin of a normal man after the start of feeding N -labeled glycine for 2 days. The dashed curve represents the change in the labeling of circulating heme, with time. The smooth curve represents the labeling of the stercobilin isolated from the feces, with time. ...

The condensation of succinate with glycine was postulated by Shemin and Russell (29) to form a-amino-/3-ketoadipic acid. This compoimd de-carboxylates spontaneously to form 3-AL (SO). 5-AL when, supplied to duck erythrocytes was shown to be incorporated into heme more readily than succinate or glycine. With labeled 8-AL the tagged C atoms were found in the predicted positions in the porphyrins by the methods described above (SI). 

Labeled glycine added to isolated intact reticulocytes from duck blood is converted to labeled heme as was first shown by Shemin et al. 20). In addition, PROTO is also formed (dS) and this compound can be determined directly by colorimetric methods. In chicken eiythrocytes supplied in vitro with excess glycine (0.05 M) about two-thirds of the newly formed porphyrin is in the form of PROTO and the rest is newly formed heme (S4)-Various members of the citric acid cycle also enhance the yield indicating that they are partially permeable to the red cell membrane 35). 

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