Enzyme kinetics: Difference between revisions

Revision as of 21:39, 23 September 2006

Revision as of 21:40, 23 September 2006

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When a set of ''v'' by [S] curves (fixed A, varying B) from an enzyme with a ternary-complex mechanism are plotted in a [[Lineweaver-Burk plot]], the set of lines produced will intersect.

Enzymes with ternary complex mechanisms include [[Glutathione S-transferase|glutathione ''S''-transferase]],<ref>Dirr H, Reinemer P, Huber R. ''X-ray crystal structures of cytosolic glutathione S-transferases. Implications for protein architecture, substrate recognition and catalytic function.'' Eur J Biochem. 1994 Mar 15;220(3):645-61. PMID 8143720</ref> [[dihydrofolate reductase]]<ref>Stone SR, Morrison JF. ''Dihydrofolate reductase from Escherichia coli: the kinetic mechanism with NADPH and reduced acetylpyridine adenine dinucleotide phosphate as substrates.'' Biochemistry. 1988 Jul 26;27(15):5493-9. PMID 3052577</ref> and [[DNA polymerase]].<ref>Fisher PA. ''Enzymologic mechanism of replicative DNA polymerases in higher eukaryotes.'' Prog Nucleic Acid Res Mol Biol. 1994;47:371-97. PMID 8016325</ref> These two links show short animations showing the mechanisms of [http://chem-faculty.ucsd.edu/kraut/dhfr.html Dihydrofolatedihydrofolate reductase] and

[http://chem-faculty.ucsd.edu/kraut/dNTP.html DNA polymerase]: two enzymes with ternary complex mechanisms.

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When a set of ''v'' by [S] curves (fixed A, varying B) from an enzyme with a ping-pong mechanism are plotted in a Lineweaver-Burk plot, a set of parallel lines will be produced.

Enzymes with ping-pong mechanisms include [[oxidoreductases]] such as [[peroxidase|thioredoxin peroxidase]]<ref>Akerman SE, Muller S. ''2-Cys peroxiredoxin PfTrx-Px1 is involved in the antioxidant defence of Plasmodium falciparum.'' Mol Biochem Parasitol. 2003 Aug 31;130(2):75-81. PMID 12946843</ref> or serine proteases such as [[trypsin]] or [[chymotrypsin]].<ref>Kraut J. ''Serine proteases: structure and mechanism of catalysis.'' Annu Rev Biochem. 1977;46:331-58. PMID 332063</ref> Serine proteases, include both digestive enzymes (trypsin, chymotrypsin, and elastase) and several enzymes of the blood clotting cascade. These proteases contain an active site serine whose hydroxyl group forms a covalent bond with a carbonyl carbon of a peptide bond, thereby causing hydrolysis of the polypeptide. This link is to a short animation showing the mechanism of [http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-2/06_21_chymotrypsin.html Chymotrypsinchymotrypsin].

== Non-Michaelis-Menten kinetics ==