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Unformatted text preview: Ch. 19 Enzymes Enzymes are t ruly incredible catalysts , as reactions may occur at a rate 10 6 (to 10 10 ) times faster with enzyme present than with no enzyme. Enzymes work at body temperature (37C) and at physiological pH (pH~7.4), not at high temperatures & pressures and with strong oxidizing/reducing agents and/or strong acids/bases as typically required in the lab. The compound(s) upon which the enzyme acts are its substrate (s). Specificity While inorganic catalysts can catalyze many similar reactions, this is generally not t rue for enzymes, as the type of specificity can vary. Absolute specificity an enzyme that catalyzes the reaction of only one substrate (e.g., urease catalyzes only the hydrolysis of urea) Relative (group or linkage) specificity a) for group specificity an enzyme catalyzes reactions of similar compounds with the same functional group, b) for linkage specificity an enzyme catalyzes the formation or breakage of only certain bonds in a molecule (e.g.,trypsin only hydrolyzes peptide bonds) Stereochemical specificity the reaction(s) for one type of enantiomer are catalyzed. Our bodies use only D-sugars and L-amino acids, so enzymes involved with digestion and metabolism often show this specificity. Systematic Classification of Enzymes The International Commission on Enzymes adopted a systematic naming of enzymes, deciding on 6 major groups according to their actions. The name begins with EC followed by an assigned 4 digit number. 1) Oxidoreductases catalyze oxidation-reduction reactions (an example is a dehydrogenase which removes hydrogen from the substrate) 2) T ransferases catalyze transfer of functional groups, e.g., -CH 3 (methyl),...
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