Basics of Biochemistry Introduction of Enzymes Ashish Kr Dwivedi, PhD
Enzymes Enzymes are biological catalysts. Recall that by definition, catalysts alter the rates of chemical reactions but are neither formed nor consumed during the reactions they catalyze. .Enzymes are the most sophisticated catalysts known .Most enzymes are proteins. Some nucleic acids exhibit enzymatic activities (e.g., rRNA). We will focus primarily on protein-type catalysts.
Enzyme Characteristics Enzymes significantly enhance the rates of reactions, by as much as - 106! .For example, the enzyme "carbonic anhydrase" accelerates the dissolution of carbon dioxide in water: While this occurs without the help of this enzyme, the enzyme increases the rate of reaction by one million times (106).
Rate Enhancement by Urease The enzyme urease enhances the rate of urea hydrolysis at pH 8.0 and 20 C by a factor of 1014. If a given quantity of urease can completely hydrolyze a given quantity of urea in 5.0 min at 20 C and pH 8.0, how long would it take for this amount of urea to be hydrolyzed under the same conditions in the absence of urease? Assume that both reactions take place in sterile systems so that bacteria cannot attack the urea. Answer Time to hydrolyze urea (5.0 min)(1014) (60 min/hr) (24 hr/day) (365 days/yr) = 9.5 108 yr - 950 million years!
lons Cu2+ Fe2+ or Fe3+ Enzymes Cytochrome oxidase Cytochrome oxidase, catalase, peroxidase Pyruvate kinase Hexokinase, glucose 6-phosphatase, Ma2+ Mn2+ Mo Ni2+ Se Zn2t+ pyruvate kinase Arginase, ribonucleotide reductase Dinitrogenase Urease Glutathione peroxidase Carbonic anhydrase, alcohol dehydrogenase, carboxypeptidases A and B
Coenzyme Biocytin Coenzyme A 5'-Deoxyadenosylcobalamin Examples of chemical groups transferred CO Acyl groups H atoms and alkyl groups Dietary precursor in mammals Biotin Pantothenic acid and other compounds Vitamin B, 12 (coenzyme B12) Flavin adenine dinucleotide Lipoate Nicotinamide adenine dinucleotide Hydride ion (:H) Pyridoxal phosphate Tetrahydrofolate Thiamine pyrophosphate Electrons Riboflavin (vitamin B2) Not required in diet Nicotinic acid (niacin) Pyridoxine (vitamin B) Folate Thiamine (vitamin B,) Electrons and acyl groups Amino groups One-carbon groups Aldehydes
Type of reaction catalyzed Transfer of electrons (hydride ions or H atoms) Group transfer reactions Hydrolysis reactions (transfer of functional groups to water) Addition of groups to double bonds, or formation of double bonds Class no. Class name Oxidoreductases Transferases Hydrolases Lyases 2 3 4 by removal of groups Transfer of groups within molecules to yield isomeric forms Formation of C-C,C-S, C-O, and C-N bonds by condensation 5 Isomerases 6 Ligases reactions coupled to cleavage of ATP or similar cofactor Enzyme Commission number (E.C. number) is 220.127.116.11. The first number (2) denotes the class name (transferase); the second number (7), the subclass (phosphotransferase); the third number (1), a phosphotransferase with a hydroxyl group as acceptor; and the fourth number (1), D -glucose as the phosphoryl group acceptor.
Ashish Kr Dwivedi
Former Scientist (IIT Kanpur), Authored 10+ Peer Reviewed International Publications, PhD (IITK) Chief Mentor Triyambak Life Sciences