Structural biochemistry carboxypeptidase

We have already seen a number of models for the zinc(II) containing enzymes such as carbonic anhydrase in Section 11.3.2. Zinc is an essential component in biochemistry, and forms part of the active site of more then 100 enzymes, of which hydrolases (such as alkaline phosphatase and carboxypeptidase A), transferases (e.g. DNA and RNA polymerase), oxidoreductases (e.g. alcohol dehydrogenase and superoxide dismutase) and lysases (carbonic anhydrase) are the most common. In addition, the non-enzyme zinc finger proteins have an important regulatory function. In many of these systems, the non-redox-active Zn2+ ion is present as a Fewis acidic centre at which substrates are coordinated, polarised and hence activated. Other roles of zinc include acting as a template and playing a structural or regulatory role. 

Kim. H. Lipscomb. W.N. Comparison of the structures of three carboxypeptidase A-phosphonate complexes determined by X-ray crystallography. Biochemistry 1991. 30. 8171-8180. 

The importance of coordination in the biochemistry of essential metallic elements may be illustrated by numerous examples of metal complexes of which the following are representative the iron complex hemoglobin and numerous enzymes containing the heme and related structures such as catalases, peroxidases and cytochromes and the iron-containing proteins ferritin, transferrin, and hemosiderin the zinc complexes zinc-insulin, carbonic anhydrase and the carboxypeptidases the cobalt complex vitamin B12 the copper complex, ceruloplasmin the molybdenum-containing enzymes, xanthine oxidase, and nitrate reductase DNA-metal ion complexes. 

Many structural biology and biochemistry studies rely on the precise identification of the N-/C-terminal sequence of a protein (e.g., signal peptide identification, determining the cleavage site and specificity of a novel protease, etc.). Digestion of proteins in arrays of carboxypeptidase Y at different concentrations with MALDl-MS-based readout can be employed to derive C-terminal sequence information for proteins. The amino-terminus of a protein can be derived by wet chemistries similar to Edman degradation coupled to MS-readout. This method of protein ladder sequencing, reported first by Kent and... 

Asano, Y, Kato, Y, Nakazawa, A., and Kondo, K., "Structural similarity of u-aminopepti-dase to carboxypeptidase DD and 3-lactamases." Biochemistry, 31,2316-2328 (1992). 

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