TAILIEUCHUNG - Biochemistry, 4th Edition P47

Biochemistry, 4th Edition P47. 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. | How Tightly Do Transition-State Analogs Bind to the Active Site 423 Solvation of charged groups on a substrate in solution releases energy making the charged substrate more stable. When a substrate with charged groups moves from water into an enzyme active site Figure the charged groups are often desolvated to some extent becoming less stable and therefore more reactive. Similarly when a substrate enters the active site charged groups may be forced to interact unfavorably with charges of like sign resulting in electrostatic destabilization Figure . The reaction pathway acts in part to remove this stress. If the charge on the substrate is diminished or lost in the course of reaction electrostatic destabilization can result in rate acceleration. Whether by strain desolvation or electrostatic effects destabilization raises the energy of the ES complex and this increase is summed in the term A Gd the free energy of destabilization Figures and . How Tightly Do Transition-State Analogs Bind to the Active Site Although not apparent at first there are other important implications of Equation . It is important to consider the magnitudes of KS and KT. The ratio ke ku may even exceed 1016 as noted previously. Given a ratio of 1016 and a typical KS of 10 1 M the value of KT should be 10 201 M. The value of KT for fructose-1 6-bisphos-phatase see Table is an astounding 7 X 10 26 M This is the dissociation constant for the transition state from the enzyme and this very low value corresponds to very tight binding of the transition state by the enzyme. It is unlikely that such tight binding in an enzyme transition state will ever be determined in a direct equilibrium measurement however because the transition state itself is a moving target. It exists only for about 10 14 to 10 13 sec less than the time required for a bond vibration. On the other hand the nature of the elusive transition state can be explored using transition-state analogs .

• Sinh học
• Nền tảng của hóa sinh học
• trao đổi chất protein
• RNA trao đổi chất
• nguyên tắc của hóa sinh
• Axit amin
• công nghệ DNA