Chapter 1 Cellular ATP

摘要: Summary ATP is a kinetically stable molecule with high free energy of hydrolysis/high phosphate transfer potential. This means it can act as common unit exchange between variety highly exergonic catabolic processes and requiring reactions within the aqueous medium cell. The chemical nature that drive wide such reactions, including movement ions proteins, dehydrations (in macromolecule biosyntheses), activation small molecules, imparting negative charge to sugars proteins. relative contributions these demand cell depends on tissue; muscle expends some 70% its turnover movements actomyosin, brain about 40% Na + transport, exocrine cells 50% biosyntheses. molecular basis for coupling hydrolysis non-chemical (e.g., contraction, ion pumping) not precisely known. A model presented in which transducing enzyme manipulate stages release from link binding changes conformational changes. rationale unifies existing schemes function enzymes, also functioning mitochondrial synthase, couples transmembrane proton flow synthesis. In humans, bulk synthesis occurs via oxidative phosphorylation mitochondria, although fuel oxidized dependent tissue. tissues (and rapidly growing tumors), however, considerable amounts are made by glycolytic conversion glucose lactate. reflects an adaptation specific functions; example, sustained contraction hence restricted O 2 supply) white or requirement biosynthetic precursors lymphocytes). levels inside maintained very (around 8 mM) under all physiological conditions increasing rate match demand. contrast, rates vary greatly (5–100-fold) demands Together, facts indicate itself cannot regulate own Cytoplasmic (glycolytic) regulated internally AMP, whose concentration amplify [ATP]; other regulators Ca 2+ cAMP, signal actual potential increased work Mitochondrial (oxidative) cytoplasmic ADP (entering adenine nucleotide translocase) and/or uniport), depending Prolonged depletion leads death, largely due development ionic osmotic imbalance. Such clinical conditions. There may be deficiencies enzymes production pyruvate kinase, dehydrogenase, dehydrogenases) lead abnormal utilization fructose intolerance, malignant hyperpyrexia, ischemia/reperfusion). resulting symptoms considerably, tissue most susceptible defect.