Enzyme (Part 1)
Key Principles Enzymes are powerful biological catalysts. Enzymes exhibit a very high degree of specificity. Enzymatic reactions occur in specialized pockets called active sites. Two concepts explain the catalytic power of enzymes. Many enzymes are regulated. ['kætəlɪst]
Enzymes In 1897, Eduard Buchner: - demonstrated cell-free yeast extracts could ferment sugar to alcohol - showed fermentation was promoted by molecules that continued to function when removed from cells
Most enzymes are proteins Catalytic activity depends on the integrity of the native protein conformation Molecular weight = ranges from 12,000 to over 1 million Some enzymes require additional chemical components: - cofactor : 1+ inorganic ions, such as Fe2+, Mg2+, Mn2+, and Zn2+ - coenzyme = complex organic or metalloorganic molecule that act as transient carriers of specific functional groups
[pæntə ‘ θenɪk ]泛酸 [ ˌraɪbə‘flevɪn ] 核黄素 [ ˌnɪkə‘tɪnɪk ] 烟碱 的 [ˌpɪrɪˈdɒksiːn ] 吡哆 醇 [‘fəʊleɪt ]叶酸 [‘θaɪəmɪn] 硫胺素 [lɪ‘pəʊt] 硫辛酸
Describing enzymes and their additional chemical components Prosthetic group = coenzyme or metal ion that is very tightly or covalently bound to the enzyme protein Holoenzyme = complete catalytically active enzyme together with its bound coenzyme and/or metal ions Apoenzyme or apoprotein = the protein part of a holoenzyme
Enzymes are classified by the reactions they catalyze Enzymes are divided into seven classes, each with subclasses, based on the type of reaction catalyzed Each enzyme has a 4-part enzyme commission number (E.C. number) and a systematic name Most enzymes have trivial names
International Classification of Enzymes Class number Class name Type pf reaction catalyzed 1 Oxidoreductase Transfer of electrons (hydride ions or H atoms) 2 Transferase Group transfer 3 Hydrolases Hydrolysis (transfer of functional groups to water) 4 Lyases Cleavage of C-C, C-O, C-N, or other bonds by elimination, leaving double bonds or rings, or addition of groups to double bonds 5 Isomerase Transfer of groups within molecules to yield isomeric forms 6 Ligases Formation of C-C, C-S, C-O, and C-N bonds by condensation reactions coupled to cleavage ofg ATP or similar cofactor 7 Translocases Movement of molecules or ions across membranes or their separation within membranes
