INTRODUCTION TO MICROBIAL PHYSIOLOGY mtner-Doudor Fig.1-10.Composite diagram of major pathways of carbohydrate metabolism.The 13 key .inside an can be harne dby the cell togenerate ATF conditions.oxygen will serve that function.but under anaerobic conditions.Eol
14 INTRODUCTION TO MICROBIAL PHYSIOLOGY Embden-Meyerhof Glucose G-6-P ATP ADP G-6-P-d-lactone 6-Phosphogluconate 2-keto-3-deoxy- 6-phosphogluconate Phosphoketolase Entner-Doudoroff Xl-5-P G-3-P E-4-P F-6-P TK SH-7-P G-3-P R-5-P Xl-5-P R-5-P Rl-5-P Xl-5-P F-6-P TA TK NADP+ NADPH + H+ F-1,6-BP Glyceraldehyde-3-P ATP ADP DOHP ATP ADP NAD+ NADH + H+ NADH + H+ Pi Phosphoenolpyruvate ATP ADP Pyruvate Lactate HCOOH + Acetate Acetaldehyde Ethanol NAD+ NADH + H+ NAD+ Glyceraldehyde-3-P Glyceraldehyde-3-P a-Acetolactate Acetyl-CoA OAA Acetate Citrate Malate Fumarate Succinate a-Ketoglutarate Oxalosuccinate Isocitrate Acetate + Acetyl CoA Glyoxylate CO2 CO2 CO2 −2H −2H −2H Acetoin Diacetyl 2,3-Butanediol 2 Acetyl CoA CO2 Acetoacetate −2H +2H C2-C3 Cleavage Phosphoketolase + Acetyl-P Acetaldehyde + Pyruvate CO2 C2-C3 Cleavage Aldolase NAD+ NADH + H+ NAD+ NADH + H+ ATP ADP Pi CO2 NADP+ NADPH + H+ Acetone Butyrate Isopropanol Butanol +2H +4H +4H CO2 Fig. 1-10. Composite diagram of major pathways of carbohydrate metabolism. The 13 key metabolites are boxed. G, glucose; E, erythrose; R, ribose; Xl, xylulose; SH, sedoheptulose; DOHP, dihydroxyacetone phosphate; OAA, oxaloacetate; TK, transketolase; TA, transaldolase. is used to pump H+ out of the cell. The resulting difference between the inside and outside of the cell in terms of charge (electrical potential) and pH (chemical potential) can be harnessed by the cell to generate ATP. Of course, in order for the cytochrome system to work, there must be a terminal electron acceptor molecule. Under aerobic conditions, oxygen will serve that function, but under anaerobic conditions, E. coli
CHEMICAL SYNTHESIS 15 三 3P-g tty Acids Murcin y (e.g.nitrate).A more Oxidation-Reduction Versus Fermentation
CHEMICAL SYNTHESIS 15 Glucose Glucose-6-P Fructose-6-P Glu-1-P Sugar Nucleotides Amino Sugars Fructose-1,6-P Dihydroxyacetone-P Glyceraldehyde-3-P Nicotinamide Coenzymes Phospholipids Glycerol-3-P 1,3 Di glycerol-P Serine Family 3 P-glycerate Serine Glycine Cysteine Tryptophan Ethanolamine 1-C Units Purine Nucleotides 2 P-glycerate Oxaloacetate Phosphoenol pyruvate CO2 Citrate Isocitrate a-Ketoglutarate Succinyl CoA Succinate Fumarate Malate Aspartate Family Aspartate Asparagine Threonine Methionine Isoleucine Pyrimidine nucleotides Nicotinamide Coenzymes Spermidine Glutamate Family Glutamate Glutamine Arginine Proline Polyamines Heme derivatives Pyruvate CO2 CO2 Acetyl CoA Fatty Acids Murein Acetate Leucine CO2 Pentose-5-P Glyceraldehyde-3-P Sedoheptulose-7-P F-6-P Erythrose 4-P Phosphoribosyl Pyrophosphate Purine Nucleotides Pyrimidine Nucleotides Histidine Tryptophan Vitamins and Cofactors Folates Riboflavin Coenzyme A Adenosylcobalamin Nicotinamide coenzymes F-6-P Glyceraldehyde-3-P Chorismate Aromatic Family Tyrosine Phenylalanine Tryptophan Vitamins and Cofactors Ubiquinone Menaquinone Folates 2-keto 3-deoxyoctonate CO2 Heptose in LPS Pyruvate Family Alanine Valine Leucine Isoleucine Lactate Ethanol Fig. 1-11. Biosynthetic pathways leading to the amino acids and related compounds. The oblong-circled intermediates are the 13 key compounds that serve as biosynthetic precursors for a variety of essential end products. has a menu of alternate electron acceptors from which it can choose depending on availability (e.g., nitrate). A more detailed accounting of this process is discussed in Chapter 9. Oxidation–Reduction Versus Fermentation Carbohydrate metabolism is the progressive oxidation of a sugar in which hydrogens are transferred from intermediates in the pathway to hydrogen-accepting molecules
INTRODUCTION TO MICROBIAL PHYSIOLOGY H+ Out CYSSTEOME MEMBRAN In H Adenosine·D-包 sine ®⊙p Phos.COOH hoenol pyruvate h小a eedoacompletdpletio be able to pass itsHalongand hrre the cell cou not regemerate NAD If this lop,the cell woul stop growing would e a d-en nding on the 1-1 common organisms
16 INTRODUCTION TO MICROBIAL PHYSIOLOGY PROTON-TRANSLOCATING ATPase H+ e− Electron Acceptor (eg. O2; Nitrate) H+ Generate Proton Motive Force H+ Adenosine - P - P Adenosine - P - P ~ P C O CH2 COOH ~ P SUSTRATE-LEVEL PHOSPHORYLATION OXIDATIVE PHOSPHORYLATION Phosphoenol pyruvate CYTOCHROME SYSTEM e− MEMBRANE Out In Fig. 1-12. Reactions essential to energy production. Oxidative phosphorylation. The energy that comprises the proton motive force can be harnessed and used to generate ATP when protons from outside the cell pass through the membrane-associated proton-translocating ATPase. The energy released will run the ATPase in reverse. It is estimated that passage of three H+ through the ATPase is required to generate one ATP. Substrate-level phosphorylation. Energy contained within high-energy phosphate bonds of certain glycolytic intermediates can be transferred to ADP, forming ATP. The example shows phosphoenolpyruvate. The most commonly used hydrogen acceptor compound is nicotinamide adenine dinucleotide (NAD) (Fig. 1-13). It is the reduced form of NAD (NADH) that passes the H+ and e− to the cytochrome system. However, a problem can develop when a cell is forced to grow in an anaerobic environment without any alternate electron acceptors. This situation could lead to a complete depletion of NAD+, with all of the NAD pool converted to NADH. NADH, produced during the early part of glycolysis, would not be able to pass its H along and therefore the cell could not regenerate NAD+. If this situation were allowed to develop, the cell would stop growing because there would be no NAD+ to continue glycolysis! To avoid this problem, many microorganisms, including E. coli, can regenerate NAD+ by allowing NADH to transfer H to what would otherwise be dead-end intermediates in the glycolytic pathway (e.g., pyruvate or acetyl CoA). The process, known as fermentation, produces lactic acid, isopropanol, butanol, ethanol, and so on, depending on the organism. E. coli does not perform all of these fermentation reactions. It is limited to lactate, acetate, formate, ethanol, CO2, and H2 production (Fig. 1-10). Table 1-1 lists the fermentation patterns for some other common organisms
CHEMICAL SYNTHESIS 17 Ribose-⊙-D-Ribose Oxi ±2 H CONH2 Ribose-D-包-Ribose (a NADH+HCyochomes ATPase P:+ADP ATP Fig.1-13.Nicotinamide to the nicotina e portion of NAD.()The hydrogen atoms can be transferred from NAD to e pg TABLE 1-1.Variation in Fermentation Products Formed from Pyruvate Organism Product(s) Sacchar Carbon dioxide,ethanol E.coli (bacteria) Lactic acid.acer
CHEMICAL SYNTHESIS 17 (b) H+ + e− +O2 ATP NADH + H Cytochromes H2O Pi + ADP ATPase (a) N N N N CONH2 NH2 Ribose P P Ribose N NH2 N H H H H N H H H H H CONH2 H+ N N N + Oxidized NAD (NAD+) + Reduced NAD (NADH + H+) 2H Ribose P P Ribose Fig. 1-13. Nicotinamide adenine dinucleotide (NAD). Function of NAD in oxidation–reduction reactions. (a) Hydrogen atoms removed from a hydrogen donor are transferred to the nicotinamide portion of NAD. (b) The hydrogen atoms can be transferred from NAD to an acceptor such as cytochrome pigments. TABLE 1-1. Variation in Fermentation Products Formed from Pyruvate Organism Product(s) Saccharomyces (yeast) Carbon dioxide, ethanol Streptococcus (bacteria) Lactic acid Lactobacillus (bacteria) Lactic acid Clostridium (bacteria) Acetone, butyric acid, isopropanol, butanol Enterobacter (bacteria) Acetone, carbon dioxide, ethanol, lactic acid E. coli (bacteria) Lactic acid, acetic acid, H2, ethanol, formic acid, carbon dioxide
18 INTRODUCTION TO MICROBIAL PHYSIOLOGY ways of carbohydrate metabolism (e.g.the phosphoketolase divine ger whereas a derivative,NAD phosphate (NADP).and are involve d in biosynthetic The Nitrogen Assimilation A major or does not contain any nitrogen,how do cells acquire it?S ome microorganisms can fix m oup to form mFigure ids.Tb rtate,I p in Chapter 14. GLUTAMATE OXALOACETATE NH2 00 COOH TRANS AMINASE OH CH2 C-NH2 CH COOH COOH -KETOGLUTARATE ASPARTATE mine groupfrom glutamic acid is
18 INTRODUCTION TO MICROBIAL PHYSIOLOGY The cell does not only catabolize glucose via glycolysis. There are alternate metabolic routes available for the dissimilation of glucose. One use for alternate pathways of carbohydrate metabolism (e.g., the phosphoketolase pathway; see Fig. 1-10) is the generation of biosynthetic reducing power. The cofactor NAD is actually divided functionally into two separate pools. NAD(H) is used primarily for catabolic reactions, whereas a derivative, NAD phosphate (NADP), and its reduced form, NADPH, are involved in biosynthetic (anabolic) reactions. The phosphoketolase pathway is necessary for the generation of the NADPH that is essential for biosynthetic reactions. Nitrogen Assimilation A major omission in our discussion to this point involves the considerable amount of nitrogen (N) needed by microorganisms. Every amino acid, purine, pyrimidine, and many other chemicals in the cell include nitrogen in their structures. Since glucose does not contain any nitrogen, how do cells acquire it? Some microorganisms can fix atmospheric nitrogen via nitrogenase to form ammonia (NH4 +) and then assimilate the ammonia into amino acids (e.g., Rhizobium). Other organisms such as E. coli must start with NH4 +. The assimilation of N involves the amidation of one of the 13 key metabolites, α-ketoglutarate, to form glutamic acid (Fig. 1-14). After assimilation into glutamate, the amino nitrogen is passed on to other compounds by transamination reactions. For example, glutamate can pass its amino group to oxaloacetate to form aspartate. From Figure 1-11, it can be seen that aspartate, like glutamate, is a precursor for several other amino acids. The subject of nitrogen assimilation is covered in depth in Chapter 14. COOH C CH2 COOH O O COOH C CH2 COOH COOH C CH2 COOH CH2 NH2 COOH C CH2 COOH NH2 a-KETOGLUTARATE GLUTAMATE OXALOACETATE ASPARTATE TRANSAMINASE CH2 Fig. 1-14. Transamination. In this example, the amine group from glutamic acid is transferred to oxaloacetate, forming aspartic acid