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INTRODUCTION

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OBJECTIVES

After studying this chapter, you should be able to:

  • Appreciate and describe the structural relationships between specific B vitamins and certain coenzymes.

  • Outline the four principal mechanisms by which enzymes achieve catalysis and how these mechanisms combine to facilitate catalysis.

  • Describe the concept of an “induced fit” and how it facilitates catalysis.

  • Outline the underlying principles of enzyme-linked immunoassays.

  • Describe how coupling an enzyme to the activity of a dehydrogenase can simplify assay of the activity of a given enzyme.

  • Identify enzymes and proteins whose plasma levels are used for the diagnosis and prognosis of a myocardial infarction.

  • Describe the application of restriction endonucleases and of restriction fragment length polymorphisms in the detection of genetic diseases.

  • Illustrate the utility of site-directed mutagenesis for the identification of aminoacyl residues that are involved in the recognition of substrates or allosteric effectors, or in the mechanism of catalysis.

  • Describe how the addition of fused affinity “tags” via recombinant DNA technology can facilitate purification of a protein expressed from its cloned gene.

  • Indicate the function of specific proteases in the purification of affinity-tagged enzymes.

  • Discuss the events that led to the discovery that RNAs can act as enzymes, and briefly describe the evolutionary concept of an “RNA world.”

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BIOMEDICAL IMPORTANCE

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Enzymes, which catalyze the chemical reactions that make life on the earth possible, participate in the breakdown of nutrients to supply energy and chemical building blocks; the assembly of those building blocks into proteins, DNA, membranes, cells, and tissues; and the harnessing of energy to power cell motility, neural function, and muscle contraction. The vast majority of enzymes are proteins. Notable exceptions include ribosomal RNAs and a handful of RNA molecules imbued with endonuclease or nucleotide ligase activity known collectively as ribozymes. The ability to detect and to quantify the activity of specific enzymes in blood, other tissue fluids, or cell extracts provides information that complements the physician’s ability to diagnose and predict the prognosis of many diseases. Further medical applications include changes in the quantity or in the catalytic activity of key enzymes that can result from genetic defects, nutritional deficits, tissue damage, toxins, or infection by viral or bacterial pathogens (eg, Vibrio cholerae). Medical scientists address imbalances in enzyme activity by using pharmacologic agents to inhibit specific enzymes and are investigating gene therapy as a means to remedy deficits in enzyme level or function.

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In addition to serving as the catalysts for all metabolic processes, their impressive catalytic activity, substrate specificity, and stereospecificity enable enzymes to fulfill key roles in additional processes related to human health and well-being. Proteases and amylases augment the capacity of detergents to remove dirt and stains, and enzymes play important roles in producing or enhancing the nutrient value of food products for both humans and animals. The protease rennin, for example, is utilized in the production of cheeses while lactase is employed to remove lactose from milk ...

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