tailieunhanh - Biochemistry, 4th Edition P46

Biochemistry, 4th Edition P46. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | Are All Enzymes Proteins 413 Antibody Molecules Can Have Catalytic Activity Antibodies are immunoglobulins which of course are proteins. Catalytic antibodies are antibodies with catalytic activity catalytic antibodies are also called abzymes a word created by combining Ab the abbreviation for antibody with enzyme. Like other antibodies catalytic antibodies are elicited in an organism in response to immunological challenge by a foreign molecule called an antigen see Chapter 28 for discussions on the molecular basis of immunology . In this case however the antigen is purposefully engineered to be an analog of the transition state in a reaction. The rationale is that a protein specific for binding the transition state of a reaction will promote entry of the normal reactant into the reactive transitionstate conformation. Thus a catalytic antibody facilitates or catalyzes a reaction by forcing the conformation of its substrate in the direction of its transition state. A prominent explanation for the remarkable catalytic power of conventional enzymes is their great affinity for the transition state in the reactions they catalyze see Chapter 14. One proof of this principle has been to prepare ester analogs by substituting a phosphorus atom for the carbon in the ester group Figure . The phosphonate compound mimics the natural transition state of ester hydrolysis and antibodies elicited against these analogs act like enzymes in accelerating the rate of ester hydrolysis as much as 1000-fold. Abzymes have been developed for a number of other classes of reactions including C C bond formation via aldol condensation the reverse of the aldolase reaction see Figure reaction 4 and Chapter 18 and the pyridoxal 5 -P-dependent aminotransferase reaction shown in Figure . This biotechnology offers the real possibility of creating specially tailored enzymes designed to carry out specific catalytic processes. Catalytic antibodies apparently occur naturally. Autoimmune