生物化学I-英文版 第七章.pptVIP

2010 Spring Chapter 7 2009 Spring Coenzymes Metal cofactors Single metal sites mostly structural sites Ca2+, Zn2+ exceptions Cu2+ Metal clusters Fe,S (Fe2S2 ,Fe4S4) FeMoco Mn4, Mn2, Cu2, mixed metal clusters Organometallic cofactors Porphyrins Cobalamin Metal chelation by amino acids Ligands are determined by electronic affinity and geometrical constraints Small, “hard” metals prefer “hard” ligands e.g. Ca2+ --- -OOC–R (Asp, Glu) Large “soft” metals prefer “soft” ligands e.g. Hg2+ --- S–R (Cys) Iron and copper in between e.g. Fe2+ --- N (His) Fig 7.2 Mechanism of carbonic anhydrase Fig. 7.2 (continued) Iron in metalloenzymes Heme iron complexes(3cyv,3cy5) porphyrin (pyrrole) ring iron prefers hexacoordination 5th coordinate position protein amino acid (usually His) 6th coordinate substrate binding or protein binding Fig 7.3 Iron-sulfur clusters (3fwy) Classification of coenzymes in mammals A. Metabolite Coenzymes Reactions of ATP SAM synthesis Fig 7.5 S-Adenosylmethionine S-Adenosylmethionine (SAM) is a methyl donor in many biosynthetic reactions Fig 7.6 Fig 7.6 (continued) B. Vitamin-Derived Coenzymes and Nutrition Table 7.1 Vitamins, nutritional deficiency diseases (avitaminosis) Understanding Vitamins Fat-Soluble vs. Water-Soluble Fat-soluble: vitamins A, D, E, K Absorbed like fat, into lymphatic system Stored in larger quantities Less vulnerable to cooking losses Water-soluble: 8 B-vitamins, vitamin C Absorbed into bloodstream Stored in small amounts Vulnerable to cooking losses Vitamins in Foods Natural sources: all food groups Enriched and fortified foods Vitamins: Vital Keys to Health Box 7.2 Vitamin C: a vitamin but not a coenzyme Functions Antioxidant Needed for collagen synthesis Food sources Fruits: citrus, strawberries, kiwi Vegetables: broccoli, tomatoes, potatoes Deficiency Scurvy Toxicity May cause GI distress/IMMUNO in high doses Functions Coenzyme in energy metabolism Supports fatty acid synthesis Food sources Whole and e