Tema 7: Homofermentative Pathway Chapter 14 Pages

Formation of acetyl-CoA from pyruvate pyruvate Acetyl-CoA + CO 2 + NADH 2 Pyruvate dehydrogenase Acetyl-CoA + CO 2 + H 2 Acetyl-CoA + formic acid Pyruvate Formate lyase Pyruvate Ferredoxin oxidoreductase Anaerobically

Pyruvate dehydrogenase 1)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 HOOC-C-CH 3 CH 3 CO-SCoA + CO 2 OO NAD NADH 2 TCA cycle HSCoA

Pyruvate Formate lyase 1)Catalyze an oxidative decarboxylation. where the electrons remain in the carbonyl group. 2) The product acetyl-CoA usually goes to acetyl-P. HOOC-C-CH 3 + CoASH CH 3 CO-SCoA + CH 2 O 2 OO CH3CO-P + HSCoA O CH3COOH + ATP PiPhosphotransacetylase Acetate kinase ADP Mg +

Pyruvate Ferredoxin oxidoreductase 1)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. HOOC-C-CH 3 + CoASH CH 3 CO-SCoA + CO 2 OO Fd ox Fd red 2H + 2H 2 hydrogenase CH 3 COOH + ATP Acetate kinase ADP Mg + CH 3 CO-P + HSCoA O Pi Phosphotransacetylase

How is acetyl-CoA made from Acetate? It is typically made as follows CH 3 COOH + ATP Acetate kinase ADP Mg + CH 3 CO-P + HSCoA O Pi Phosphotransacetylase CH 3 CO-SCoA O acetylCoA synthetase or INOUT Carbon and energy

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

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.

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

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

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

Lactate dehydrogenase

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.

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.

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”

Vitamin forms: Niacin Nutritional disease: pellagra

Nicotinamide Adenine Dinucleotide

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.

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.