9/15/2014 Coenzymes BCMB 3100 ‐ Introduction to Coenzymes & Vitamins Some enzymes require _________ for activity •Cofactors (1) _______________ (mostly metal ions) •Essential ions (2) _____________ (organic compounds) •Coenzymes •Cosubstrates Apoenzyme + Cofactor •Prosthetic groups Holoenzyme (protein only) •Coenzymes structure/function/active group (active) (inactive) •Vitamins 1 Metal ions have diverse functions in enzymes • Participate in ____________, generally tightly bound to enzyme, function e.g. as electrophilic catalysts or aid in generating a nucleophile Coenzymes • Coenzymes act as group-transfer reagents • Hydrogen, electrons, or other groups can be transferred • Two types of coenzymes: ___________________ • Participate in _________________ at the active site • ________________________ 1 9/15/2014 The pyruvate dehydrogenase complex requires 4 coenzymes Types of cofactors Ca++ K+ Mg++ Mn++ Fe-S center zinc copper cobalt See: *pg. 126 for info on metal ions in catalysis *Table 15.2 (page 261) as summary table for coenzymes *ATP * SAM UDP-sugar * FMN/FAD * TPP * PLP * Biotin * NAD+/NADP+ * tetrahydrofolate * adenosyl/methyl* CoA cobalamin * ubiquinone * Lipoic acid/ * protein coenzymes lipoamide http://www.nd.edu/~aseriann/pyrde.html 5 Coenzyme Classification • There are two classes of coenzymes (1) ____________ are altered during the reaction and regenerated by another enzyme (2) _________________ remain bound to the enzyme during the reaction, and may be covalently or tightly bound to enzyme 7 8 2 9/15/2014 S‐Adenosylmethionine (SAM) SAM is the donor of methyl groups for most biosynthetic reactions S-Adenosylmethionine + X S-Adenosylhomocysteine + X-CH3 Activated methyl group in red Example: SAM donates the methyl group for the synthesis of the hormone epinephrine from norepinephrine SAM SAHC 9 UDP‐sugar: activated form of sugars used as substrate in many biosynthetic reactions 10 A third example of a cosubstrate coenzyme Fig. 15.3 Nucleotide-sugars are cosubstrates in many glycosylation reactions 11 3 9/15/2014 Some coenzymes require vitamins as part of their structure __________: organic substance required in trace amounts for a number of essential biochemical reactions Not all vitamins are part of coenzymes; only some are Table 15‐4 Some vitamins are ___________ • Four lipid vitamins: A, D, E, K • All contain rings and long, aliphatic side chains • All are highly hydrophobic • The lipid vitamins differ widely in their functions Vitamin‐Derived Coenzymes • Vitamins: required for synthesis of some coenzymes, must be obtained from nutrients • Animals rely on plants, meat, & microorganisms for vitamin sources • Most vitamins must be enzymatically transformed to make the coenzyme (e.g. some water soluble vitamins) • BE SURE TO LEARN WHICH VITAMINS ARE PART OF WHICH COENZYMES (Tables 15.2 & 15.3) 16 4 9/15/2014 Vitamins, nutritional deficiency diseases (see Table 15.3 and Appendix D) Vitamin C: a vitamin but not a coenzyme Vitamin Disease Ascorbate (C) Nicotinic acid (B3) Riboflavin (B2) Pantothenate (B53) Thiamine (B1) Pyridoxal (B6) Biotin Folate Cobalamin (B12) Scurvy Pellagra Growth retardation Dermatitis in chickens Beriberi Dermatitis in rats Dermatitis in humans Anemia, spina bifida Pernicious anemia • A reducing reagent for hydroxylation of collagen • Deficiency leads to the disease scurvy • Most animals (not primates) can synthesize Vit C 17 18 Group Activity on Coenzymes Be sure to read through “Hints for You must learn to recognize the major coenzymes learning coenzymes” as you prepare and teach your coenzymes to your group. Be sure to work in your groups to learn the co-enzymes over the next week. 5 9/15/2014 Types of cofactors * 2 electrons 1 or 2 electrons 1 or 2 electrons Ca++ K+ Mg++ Mn++ Fe-S center zinc copper cobalt See: *pg. 126 for info on metal ions in catalysis *Table 15.2 as summary table for coenzymes *ATP * SAM UDP-sugar 2 carbon groups containing carbonyl * FMN/FAD * TPP * PLP * Biotin * NAD+/NADP+ * tetrahydrofolate * adenosyl/methyl* CoA cobalamin * ubiquinone * Lipoic acid/ protein coenzymes ATP‐dependent carboxylation *ATP may also donate pyrophosphoryl and adenosyl groups lipoamide NAD+ 2 carbon groups containing carbonyl NOTE: Electron carrier in many oxidation reduction reactions; used for reactions in pathways that lead to generation of ATP Nicotinamide adenine dinucleotide _____________________ Fig. 15‐12a 6 9/15/2014 Flavine adenine dinucleotide _______________ Nicotinamide adenine dinucleotide phosphate __________________ FAD NOTE: Electron donor in most reductive biosynthesis reactions Fig. 15.15 Fig. 15.13 FAD FADH2 Example of reduced substrate Example of oxidized product Fig. 15.14 Pg. 258 7 9/15/2014 Coenzyme A Fig. 15.16 Fig. 15.17 Coenzyme A Pyridoxal phosphate (carrying an acetyl group during a reaction) Fig. 18.1 See pg. 545 8 9/15/2014 cobalamin See pgs. 319‐321 Ubiquinone (Coenzyme Q) See Appendix D Group Activity on Coenzymes Be sure to read through “Hints for learning coenzymes” as you prepare and teach your coenzymes to your group. See Pg. 356 Be sure to work in your groups to learn the co-enzymes over the next week. 9
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