1-carbon metabolism

Some catabolic reactions of amino acid carbon chains are easy transformations to and from TCA cycle intermediates—for example, the transamination of alanine to pyruvate. Reactions involving 1-carbon units, branched-chain, and aromatic amino acids are more complicated. This chapter starts with 1-carbon metabolism and then considers the catabolic and biosynthetic reactions of a few of the longer side chains. Amino acid metabolic pathways can present a bewildering amount of material to memorize. Perhaps fortunately, most of the more complicated pathways lie beyond the scope of an introductory course or a review such as this. Instead of a detailed listing of pathways, this chapter concentrates on general principles of amino acid metabolism, especially those that occur in more than one pathway. 

---

This is not the place to expose in detail the problems and the solutions already obtained in studying biochemical reaction networks. However, because of the importance of this problem and the great recent interest in understanding metabolic networks, we hope to throw a little light on this area. Figure 10.3-23 shows a model for the metabolic pathways involved in the central carbon metabolism of Escherichia coli through glycolysis and the pentose phosphate pathway [22]. 

M. Gibbs and E. Lat2ko, eds.. Photosynthesis 11 Photosynthetic Carbon Metabolism and Kelated Processes, Tnyclopedia of Plant Physiology, N.S., Springer-Vedag, Berlin, 1979. 

BOTH RIBOSE-5-P AND NADPH ARE NEEDED BY THE CELL In this case, the first four reactions of the pentose phosphate pathway predominate (Figure 23.37). N/VDPH is produced by the oxidative reactions of the pathway, and ribose-5-P is the principal product of carbon metabolism. As stated earlier, the net reaction for these processes is... 

Dazlich, D. A. (1996a). Simulations of terrestrial carbon metabolism and atmospheric CO2 in a general circulation model. Part 1 Surface carbon fluxes, Telliis, Ser. B, 48,521-542. 

Valentini, R., Scarascia Mugnozza, G.E., De Agnelis, P. and Matteucci, G. 1995 Coupling water and carbon metabolism of natural vegetation at integrated time and space scales. Agricultural and Forest Meteorology 73 297-306. 

Hokum, J.A.M. Winter, K. (1982). Activity of enzymes of carbon metabolism during the induction of Crassulacean acid metabolism in Mesembryanthemum crystallinum L. Planta, 155, 8-16. 

NAD and NADP and FMN and FAD, respectively. Pantothenic acid is a component of the acyl group carrier coenzyme A. As its pyrophosphate, thiamin participates in decarboxylation of a-keto acids and folic acid and cobamide coenzymes function in one-carbon metabolism. 

Shane B Folylpolyglutamate synthesis and role In the regulation of one-carbon metabolism. Vitam Horm 1989 45 263. 

P. Bottner, Z. Sallih, and G. Billes, Root activity and carbon metabolism in soils. Biol. Fertil. Soils 7 71 (1988). 

T. Person, E. Baiith, M. Clarholm, H. Lundkvist, B. E. Soderstrom, and B. Sohlen-ius. Trophic structure, biomass dynamics and carbon metabolism of soil organisms in a Scots pine fore.st. Ecol. Bull. i2 4l9 (1980). 

I. Jakobsen, Carbon metabolism in myeorrhiza. Methods Microbiol. 23 149 (1991). 

The dihydrofolate reductase enzyme (DHFR) is involved in one-carbon metabolism and is required for the survival of prokaryotic and eukaryotic cells. The enzyme catalyzes the reduction of dihydrofolate to tetrahydrofolate, which is required for the biosynthesis of serine, methionine, purines, and thymidylate. The mouse dihydrofolate reductase (mDHFR) is a small (21 kD), monomeric enzyme that is highly homologous to the E. coli enzyme (29% identify) (Pelletier et al., 1998). The three-dimensional structure of DHFR indicates that it is comprised of three structural fragments F[l], F[2] andF[3] (Gegg etal., 1997). 

Butler, M.J., Bruheim, P, Jovetic, S. et al. (2002) Engineering of primary carbon metabolism for improved antibiotic production in Streptomyces lividans. Applied and Environmental Microbiology, 68, 4731 4739. 

The yield coefficient of the poly(3HB) synthesis determined solely from carbon metabolism can easily be calculated if the metabolic sequence from the carbon substrate to poly(3HB) C4H602 is known, for instance ... 

CMD = carbon metabolism determined, i.e., energetically independent. a This range results from differences in possible energy gains derived from the oxidation of formaldehyde. 

Connections To folate metabolism and one-carbon metabolism in de novo synthesis. 

Marques, I.A. and L.E. Anderson. 1986. Effects of arsenite, sulfite, and sulfate on photosynthetic carbon metabolism in isolated pea (Pisum sativum L., cv Little Marvel) chloroplasts. Plant Physiol. 82 488-493. 

---