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Tema 7: Homofermentative Pathway

Tema 7: Homofermentative Pathway. Chapter 14 Pages 383 - 402. Acetyl-CoA + CO 2 + NADH 2. Acetyl-CoA + formic acid. Acetyl-CoA + CO 2 + H 2. Anaerobically. Formation of acetyl-CoA from pyruvate. Pyruvate dehydrogenase. pyruvate. Pyruvate Ferredoxin oxidoreductase. Pyruvate

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Tema 7: Homofermentative Pathway

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  1. Tema 7: Homofermentative Pathway • Chapter 14 • Pages 383 - 402

  2. Acetyl-CoA + CO2 + NADH2 Acetyl-CoA + formic acid Acetyl-CoA + CO2 + H2 Anaerobically Formation of acetyl-CoA from pyruvate Pyruvate dehydrogenase pyruvate Pyruvate Ferredoxin oxidoreductase Pyruvate Formate lyase

  3. Pyruvate dehydrogenase • Catalyze an oxidative decarboxylation. • 2) It is found in aerobically grown Bacteria, mitocondria, but • not in Archaea. • 3) The product acetyl-CoA usually goes to the TCA cycle • instead of to acetyl-P HSCoA O O HOOC-C-CH3 CH3CO-SCoA + CO2 NAD NADH2 TCA cycle

  4. Pyruvate Formate lyase • Catalyze an oxidative decarboxylation. • where the electrons remain in the carbonyl group. • 2) The product acetyl-CoA usually goes to acetyl-P. O O HOOC-C-CH3 + CoASH CH3CO-SCoA + CH2O2 Pi Phosphotransacetylase ADP O Mg+ CH3CO-P + HSCoA CH3COOH + ATP Acetate kinase

  5. O O HOOC-C-CH3 + CoASH CH3CO-SCoA + CO2 Fd ox Fd red Pi hydrogenase Phosphotransacetylase • Catalyze an oxidative decarboxylation where ferredoxin • is the Electron acceptor. • 2) It is found typically in clostridia and sulfate reducing bacteria • (SRB) and other anaerobes. • 3) The product acetyl-CoA usually goes to acetyl-P. Pyruvate Ferredoxin oxidoreductase 2H+ 2H2 O ADP Mg+ CH3COOH + ATP CH3CO-P + HSCoA Acetate kinase

  6. O CH3CO-SCoA How is acetyl-CoA made from Acetate? It is typically made as follows O ADP Mg+ CH3COOH + ATP CH3CO-P + HSCoA Acetate kinase or Phosphotransacetylase acetylCoA synthetase Pi OUT IN Carbon and energy

  7. Lactic Acid Bacteria • Characteristics: Gram positive, carbohydrate users, proteolysis rare, nonmotile, non-spore forming • Strict fermentors, • unable to synthesize cytochromes unless heme is added. • catalase negative • oxidase negative • Nutritionally fastidious • All make lactic acid (lactate) as predominant end product

  8. Lactic Acid Bacteria • Types of fermentation • Homofermentative: glucose to 2 lactic acids, 85-95% of glucose carbon in lactate • Heterofermentative: glucose to 1 lactate, 1 ethanol, and 1 carbon dioxide, only 50% or less of glucose carbon in lactate. • Types of products will define the pathway used and ATP made.

  9. Lactic Acid Bacteria • Types of organisms • Streptococcus: homofermentative • Leuconostoc: heterofermentative • Pediococcus homofermentative • Lactobacillus; heterofermentative or homofermentative.

  10. Lactic Acid Bacteria • Streptococcus species: • Enterococcus: gut dwellers • Lactococcus • natural fermentations • Lactic acid production: lowers pH, preserves and precipitates proteins

  11. Lactic acid bacteria • Homofermentative pathway • Uses Glycolytic pathway to make 2 pyruvates from glucose • Overview: • Activation-use 2 ATP • Make ß-carbonyl • C-C bond cleavage • Oxidation/reduction • Substrate-level phosphorylation

  12. Lactate dehydrogenase

  13. Isomerization Reaction: Creates an electron attracting keto group at the # 2 carbon • H dissociates from C2 • 2 electrons shift to form cis enediol • H from hydroxyl group dissociates • 2 electrons shift to form keto group. • Forces electrons in enol bond to shift to C1.

  14. C-C bond cleavage: Aldolase Reaction H dissociates from C4; 2 electrons shift to form cis enediol H from hydroxyl group (C4) dissociates 2 electrons shift to form keto group. Forces electrons in enol bond to shift to C1.

  15. Coenzymes (cofactors)/Vitamins • Some are bound to enzyme • Apoenzyme + cofactor give holoenzyme • Metal ion, organic cofactors • Some are soluble • Act as co-substrate • Pyruvate + NADH + H+ --> lactate + NAD+ • Vitamins: • Portion of cofactor that cell can’t make, must be in diet • “Vital amine”

  16. Vitamin forms: Niacin Nutritional disease: pellagra

  17. Nicotinamide Adenine Dinucleotide

  18. NAD functions • Function: oxidation reduction reaction, accepts hydride anion (H-): one proton and two electrons • That’s why we write NADH + H + • Biosynthesis uses NADP+ most often • Catabolism uses NAD+ most often.

  19. In conclusion Streptococcus • Uses glycolysis to degrade glucose to 2 pyruvates • NADH’s made in pathway are reoxidized by reducing pyruvate to lactate • NADH is key cofactor in oxidation reduction reactions • ATP made solely by substrate level phosphorylation.

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