《生物化学》课程PPT教学课件（英文版）Chapter 8 Enzyme Catalysis

Chapter 8 Enzyme Catalysis Homework Il(contd): Chapter 8, Problems 5,7,8,9,1l( the diagonal line with“ Slope”is the blue line), 12, 16, 17 Due October 25(Wed)

Chapter 8 Enzyme Catalysis Homework II (cont’d): Chapter 8, Problems 4, 5, 7, 8, 9, 11 (the diagonal line with “Slope” is the blue line), 12, 16, 17 Due October 25 (Wed)

1. Enzymes were among the first biological macromolecules to be studied chemically 1.1 Much of the early history of biochemistry is the history of enzyme research. 1.1.1 Biological catalysts were first recognized in studying animal food digestion and sugar fermentation with yeast(brewing and wine making). 1.2 Ferments(i. e,, enzymes, meaning in “ in yeast”) were thought( wrongly)tobe separable from living yeast cells for quite some time (Louis Pasteur)

1. Enzymes were among the first biological macromolecules to be studied chemically 1.1 Much of the early history of biochemistry is the history of enzyme research. 1.1.1 Biological catalysts were first recognized in studying animal food digestion and sugar fermentation with yeast (brewing and wine making). 1.1.2 Ferments (i.e., enzymes, meaning in “in yeast”) were thought (wrongly) to be inseparable from living yeast cells for quite some time (Louis Pasteur)

1.1.3 Yeast extracts were found to be able to ferment sugar to alcohol(eduard Buchner, 1897, who won the nobel prize in Chemistry in 1907 for this discovery ). 1.1.4 Enzymes were found to be proteins(1920s to 1930s. James Sumner on urease and catalase. all enzymes are proteins, John Northrop on pepsin and trypsin, both shared the 1946 Nobel prize in Chemistry). 1.1.5 Almost every chemical reaction in a cell is catalyzed by an enzyme(thousands have been purified and studied, many more are still to be discovered 1.1.6 Proteins do not have the absolute monopoly on catalysis in cells. Catalytic RNa were found in the 1980sThomas Cech, Nobel Prize in Chemistry in 1989)

1.1.3 Yeast extracts were found to be able to ferment sugar to alcohol (Eduard Buchner, 1897, who won the Nobel Prize in Chemistry in 1907 for this discovery). 1.1.4 Enzymes were found to be proteins (1920s to 1930s, James Sumner on urease and catalase, “all enzymes are proteins”, John Northrop on pepsin and trypsin, both shared the 1946 Nobel Prize in Chemistry). 1.1.5 Almost every chemical reaction in a cell is catalyzed by an enzyme (thousands have been purified and studied, many more are still to be discovered!) 1.1.6 Proteins do not have the absolute monopoly on catalysis in cells. Catalytic RNA were found in the 1980s (Thomas Cech, Nobel Prize in Chemistry in 1989)

2. The most striking characteristics of enzymes are their immense catalytic power and high specificity. 2.1 Enzymes accelerate reactions s by factors of at least a million 2.1.1 Most reactions in biological systems do not occur at perceptible rates in the absence of enzymes. 2.1.2 The rate enhancements (rate with enzyme catalysis divided by rate without enzyme catalysis) brought about by enzymes are often in the range of 107to1014) 2.1.3 For carbonic anhydrase, an enzyme +H*), the rate enhancement is(h,o+co,->Hco3 catalyzing the hydration of co is 10(each enzyme molecule can hydrate 105 molecules of co2 per second

2. The most striking characteristics of enzymes are their immense catalytic power and high specificity. 2.1 Enzymes accelerate reactions by factors of at least a million. 2.1.1 Most reactions in biological systems do not occur at perceptible rates in the absence of enzymes. 2.1.2 The rate enhancements (rate with enzyme catalysis divided by rate without enzyme catalysis) brought about by enzymes are often in the range of 107 to 1014) 2.1.3 For carbonic anhydrase, an enzyme catalyzing the hydration of CO2 (H2O + CO2 → HCO3 - + H+ ), the rate enhancement is 107 (each enzyme molecule can hydrate 105 molecules of CO2 per second!)

2.2 Enzymes are highly specific both in the reaction catalyzed and in their choice of substrates (i.e, reactants). 2.2.1 An enzyme usually catalyzes a single chemical reaction or a set of closely related reactions(side reactions leading to the wasteful formation of by-products rarely occur) 2.2.2 Enzymes exhibit various degrees of specificity in accord with their physiological functions(what of the following? ): Low specificity: some peptidases, esterases and phosphatases Intermediate specificity: hexokinase, alcohol dehydrogenases, trypsin. Absolute or near a bsolute specificity: Many enzymes belong to this group, and in extreme cases, stereochemical specificity is exhibited (i.e, enantiomers are distinguished as substrates or products )

2.2 Enzymes are highly specific both in the reaction catalyzed and in their choice of substrates (i.e., reactants). 2.2.1 An enzyme usually catalyzes a single chemical reaction or a set of closely related reactions (side reactions leading to the wasteful formation of by-products rarely occur). 2.2.2 Enzymes exhibit various degrees of specificity in accord with their physiological functions (what of the following?): Low specificity: some peptidases, esterases, and phosphatases. Intermediate specificity: hexokinase, alcohol dehydrogenases, trypsin. Absolute or near absolute specificity: Many enzymes belong to this group, and in extreme cases, stereochemical specificity is exhibited (i.e., enantiomers are distinguished as substrates or products)

2.3 Most enzymes are proteins 2.3. 1 Some enzymes require no other chemical groups other than their amino acid residues for activity. (e.g) 2.3.2 Other enzymes require additional chemical components called prosthetic groups(covalently bound) (or cofactors). 2.3.3 Prosthetic groups could be inorganic metal ions(e.g, Fe2+, Mg2+, Mn2+, Zn2+)or complex organic or metalloorganic molecules called coenzymes 2.3. 4 a complete catalytically active enzyme (including its prosthetic group) is called a holoenzyme 2.3.5 The protein part of an enzyme(without its prosthetic group) is called the apoenzyme

2.3 Most enzymes are proteins. 2.3.1 Some enzymes require no other chemical groups other than their amino acid residues for activity. (e.g.) 2.3.2 Other enzymes require additional chemical components called prosthetic groups (covalently bound) (or cofactors). 2.3.3 Prosthetic groups could be inorganic metal ions (e.g., Fe2+, Mg2+, Mn2+, Zn2+) or complex organic or metalloorganic molecules called coenzymes. 2.3.4 A complete catalytically active enzyme (including its prosthetic group) is called a holoenzyme. 2.3.5 The protein part of an enzyme (without its prosthetic group) is called the apoenzyme

2.3.6 Coenzymes often function as transient carriers of specific(functional groups during catalysis 2.3.7 Many vitamins, organic nutrients required in small amounts in the diet, are precursors of coenzymes

2.3.6 Coenzymes often function as transient carriers of specific (functional) groups during catalysis. 2.3.7 Many vitamins, organic nutrients required in small amounts in the diet, are precursors of coenzymes

able 8-5 Some Rate Enhancements produced by Enzymes Cyclophilin 10 Carbonic anhydrase 10 Triose phosphate isomerase 10 Carboxypeptidase A 10 Phosphoglucomutase 1012 Succinyl-CoA transferase 1013 Urease 1014 Orotidine monophosphate decarboxylase 10

table 8-1 Some Inorganic Elements That Serve as Cofactors for Enzymes C Cytochrome oxidase Fe Cytochrome oxidase, catalase, peroxidase Pyruvate kinase Hexokinase, glucose 6-phosphatase, pyruvate kinase M Arginase, ribonucleotide reductase Mo Dinitrogenase Urease Se Glutathione peroxidase Zn Carbonic anhydrase, alcohol dehydrogenase, carboxypeptidases A and B

table 8-2 Some Coenzymes That Serve as Transient Carriers of Specific Atoms or Functional groups* Examples of chemical Dietary precursor in Coenzyme groups transferred mammaLs Biocytin Biotin Coenzyme A Acyl groups Pantothenic acid and other compounds 5-Deoxyadenosylcobalamin H atoms and Vitamin B 12 coenzyme B12) alkyl groups Flavin adenine dinucleotide Electrons Riboflavin(vitamin B2) Lipoate Electrons and Not required in diet acyl groups Nicotinamide adenine Hydride ion(: H Nicotinic acid(niacin) dinucleotide yridoxal phosphate Amino groups Pyridoxine (vitamin B6) Tetrahydrofolate One-carbon groups Folate Thiamine pyrophosphate Aldehydes Thiamine (vitamin B,) "The structure and mode of action of these coenzymes are described in Part Ill of this book