北京大学.生物化学.2005 (4).ppt

Chapter 23, Hormonal Regulation and Integration of Mammalian Metabolism ★Specialized metabolism of major organs and tissues: the division of labor; ★Coordination of metabolism for different organs via hormones. ★ Responding to changing external conditions. ★ Meeting the demands of growth and reproduction. Metabolism is regulated at different levels At the level of the individual cells: Regulation of enzyme activities by substrate availability, allosteric mechanisms, covalent modifications. At the level of the whole organism: Chemical messengers of the neuroendocrine system, neurotransmitters and hormones. Fuel metabolism of different organs is coordinated through various hormones Insulin, glucagon, and epinepherine have been found to interplay in coordinating fuel metabolism in muscle, liver, and adipose tissue, thus keeping the blood glucose level near 4.5 mM. Insulin signals high blood glucose (acts mainly on liver, muscle and adipose tissues). Glucagon signals low blood glucose (acts mainly on liver and adipose tissues). Epinepherine signals impending activity (acts on muscle, liver and adipose tissues). In untreated diabetes, insulin is either not produced (Type I or IDDM) or is not recognized by the tissues (Type II or NIDDM), and the uptake of blood glucose is compromised.High level of glucose in blood and urine; production and excretion of ketone bodies. Hormones are chemical messengers secreted by certain tissues into the blood or institial fluid, serving to regulate the activity of other tissues. Hormones, extremely potent, are often present in extremely low concentrations and a bioassay must be established before their discovery and characterization. For instance, insulin was discovered as a substance affecting the volume and composition of urine produced by a dog (Banting, Macleod and Collip, 1920s). Radioimmunoassya (RIA) was an extremely sensitive quantitative method developed to assay peptide hormones (Yalow, 1970s) Antibodies binding to a hormone s