Ii the natural catalysts table 21 lists

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II. THE NATURAL CATALYSTS Table 2.1 lists metalloenzymes that catalyze hydrolytic and related reactions. According to the above guidelines the hydrolysis of peptide bonds is catalyzed by enzymes called peptidases that belong to the class of hydrolases (according to the official enzyme classification). Two peptidases (carboxypeptidase and thermolysin) are known in great detail, because their structures have been elu- cidated by high-resolution x-ray crystallography. They share many features; e.g., their metal ions coordinate to the same kind of protein residues. A discussion of the possible mechanism of carboxypeptidase A will be given in Section V.A. Metallopeptidases are zinc enzymes: generally they are single polypeptide chains with molecular weights in the range 30 to 40 kDa. Metallohydrolases of carbox- ylic and phosphoric esters are also often zinc enzymes. Alkaline phosphatase will be described in Section V.B as a representative of this class. Magnesium is sometimes involved in hydrolytic reactions. This is common when phosphate groups are involved, probably because the affinity of Mg2+ for phosphate groups is high. I However, hydrolytic reactions can be performed by other systems (not treated here) like urease, which contains nickel(II),z or acid phosphatase, which contains two iron ions, 3 or aconitase, which contains an Fe4S4 cluster.4
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II. THE NATURAL CATALYSTS Table 2.1 Representative metalloenzymes catalyzing hydrolytic and related reactions. 39 Enzyme Carboxypeptidase Leucine aminopeptidases Dipeptidase Neutral protease Collagenase Phospholipase C f3-Lactamase II Thermolysin Alkaline phosphatase Carbonic anhydrase a-Amylase Phospholipase A 2 Inorganic pyrophosphatase ATPase Na + -K + -ATPase Mg 2+ -Ca 2+ -ATPase Phosphatases Creatine kinase Pyruvate kinase Phosphoglucomutase DNA polymerase Alcohol dehydrogenase Metal(s) Zn 2 + Zn2+ Zn 2+ Zn 2+, Ca 2+ Zn 2 + Zn 2 + Zn 2+ Zn 2+, Ca 2+ Zn 2+, Mg2+ Zn 2 + Ca 2+, Zn 2+ Ca2+ Mg 2 + Mg 2 + Na +, K + Mg 2 +, Ca 2+ Mg 2+, Zn 2+ M 2 + M +, M 2 + Mg 2 + Mg 2 + (Mn 2+) Zn 2 + Function Hydrolysis of C-terminal peptide residues Hydrolysis of leucine N-terminal peptide residues Hydrolysis of dipeptides Hydrolysis of peptides Hydrolysis of collagen Hydrolysis of phospholipids Hydrolysis of f3-lactam ring Hydrolysis of peptides Hydrolysis of phosphate esters Hydration of CO 2 Hydrolysis of glucosides Hydrolysis of phospholipids Hydrolysis of pyrophosphate Hydrolysis of ATP Hydrolysis of ATP with transport of cations Hydrolysis of phosphate esters Phosphorylation of creatine Dephosphorylation of phosphoenolpyruvate Phosphate transfer converting glucose-I-phosphate to glucose-6-phosphate Polymerization of DNA with formation of phosphate esters Hydride transfer from alcohols to NAD + Examples of enzymes catalyzing nucleophilic addition of OH - (other than hydrolysis) and H - are carbonic anhydrase and alcohol dehydrogenase. Both are zinc enzymes. In the official biochemical classification of enzymes, carbonic anhydrase belongs to the class of lyases. Lyases are enzymes that cleave C-C, C-O, C-N,
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