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Lecture Principles of biochemistry - Chapter 7 (part 1): Cofactors

In this chapter, students will be able to understand: Understand what are essential Ions Cofactors; understand how metal ions can function as electrophiles in active site; define coenzyme, cosubstrate, prosthetic group, metabolite coenzymes, Vitamin; know what Vitamin corresponds to what coenzyme;. | Chapter 7 (part 1) Cofactors Cofactors Cofactors are organic or inorganic molecules that are required for the activity of a certain conjugated enzymes Apoenzyme = enzyme (-) cofactor Holoenzyme = enzyme (+) cofactor Inorganic cofactors – essential ions Organic cofactors – coenzymes Essential Ion Cofactors Activator ions – bind reversibly to enzyme and often participate in substrate binding. Metal ions of metalloenzymes – cations that are tightly bound to enzyme and participate directly in catalysis (Fe, Zn, Cu, Co). Metal activated enzymes – require or are stimulated by addition of metal ions (i.e. Mg2+, is required by many ATP requiring enzymes) Metal ions can function as electrophiles in active site Zinc protease (angiotensin converting enzyme) Coenzymes Cosubstrates- - altered in rxn and regenerated to original structure in subsequent rxn - disassociated from active site - shuttle chemical groups among different enzyme rxns. Prosthetic groups- - remains bound to enzyme - must . | Chapter 7 (part 1) Cofactors Cofactors Cofactors are organic or inorganic molecules that are required for the activity of a certain conjugated enzymes Apoenzyme = enzyme (-) cofactor Holoenzyme = enzyme (+) cofactor Inorganic cofactors – essential ions Organic cofactors – coenzymes Essential Ion Cofactors Activator ions – bind reversibly to enzyme and often participate in substrate binding. Metal ions of metalloenzymes – cations that are tightly bound to enzyme and participate directly in catalysis (Fe, Zn, Cu, Co). Metal activated enzymes – require or are stimulated by addition of metal ions (i.e. Mg2+, is required by many ATP requiring enzymes) Metal ions can function as electrophiles in active site Zinc protease (angiotensin converting enzyme) Coenzymes Cosubstrates- - altered in rxn and regenerated to original structure in subsequent rxn - disassociated from active site - shuttle chemical groups among different enzyme rxns. Prosthetic groups- - remains bound to enzyme - must return to original form Both cosubstrates and prosthetic groups supply reactive groups not present on amino acid side chains Metabolite coenzymes – synthesized from common metabolites Nucleoside triphosphates – (ATP) can donate phosphates, pyrophosphates, adenosyl grroups S-adenosylmethionine (SAM) – donates methyl groups Nucleotide sugars (uridine diphosphate glucose = UDP-glucose) - transfer sugars in carbohydrate metabolism Coenzymes Vitamin derived coenzymes Must be obtained from diet Synthesized by microorganisms and plants Vitamin deficiencies lead to disease state Most vitamins must be enzymatically transformed to function as a coenzyme Vitamins Vitamin Coenzyme Ascorbic acid (C) not a coenzyme Niacin NAD(P)+/NAD(P)H Riboflavin (B2) FMN & FAD Thiamin (B1) Thiamin-pyrophosphate Pyridoxal (B6) Pyridoxal phosphate Biotin Biotin Folate Tetrahydrafolate Cobalamin (B12) adenosyl-and methylcobalamin Vitamin A Retinal Vitamin K Vitamin K Pantothenate (B3) Coenzyme A Niacin (nicotinic acid) .