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Isoenzymes. R ole of cofactors and coenzyme vitamins in the catalytic action of enzymes. Coenzymes. Coenzymes act as group-transfer reagents Hydrogen, electrons, or groups of atoms can be transferred. Coenzyme classification. - PowerPoint PPT Presentation
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Isoenzymes. RIsoenzymes. Role of cofactors and ole of cofactors and coenzyme vitamins in the catalytic coenzyme vitamins in the catalytic
action of enzymes.action of enzymes.
Coenzymes
• Coenzymes act as group-transfer reagents
• Hydrogen, electrons, or groups of atoms can be transferred
Coenzyme classification
(1) Metabolite coenzymes - synthesized from common metabolites
(2) Vitamin-derived coenzymes - derivatives of vitamins
Vitamins cannot be synthesized by mammals, but must be obtained as nutrients
Examples of metabolite coenzymes
ATP
S-adenosylmethionine
ATP can donate phosphoryl group
S-adenosylmethioninedonates methyl groups in many biosynthesis reactions
Cofactor of nitric oxide synthase
5,6,7,8 - Tetrahydrobiopterin
Vitamin-Derived Coenzymes
•Vitamins are required for coenzyme synthesis and must be obtained from nutrients
•Most vitamins must be enzymatically transformed to the coenzyme
•Deficit of vitamin and as result correspondent coenzyme results in the disease
• Nicotinic acid (niacin) an nicotinamide are precursor of NAD and NADP
• Lack of niacin causes the disease pellagra
NAD+ and NADP+
NAD and NADP are coenzymes for dehydro-genases
FAD and FMN• Flavin adenine dinucleotide (FAD) and Flavin
mononucleotide (FMN) are derived from riboflavin (Vit B2)
• Flavin coenzymes are involved in oxidation-reduction reactions
FMN (black), FAD (black/blue)
Thiamine Pyrophosphate (TPP)
• TPP is a derivative of thiamine (Vit B1)
• TPP participates in reactions of: (1) Oxidative decarboxylation(2) Transketo-lase enzyme reactions
Pyridoxal Phosphate (PLP)• PLP is derived from Vit B6 family of vitamins
PLP is a coenzyme for enzymes catalyzing reactions involving amino acid metabolism (isomerizations, decarboxylations, transamination)
Enzymes active sites
Active site – specific region in the enzyme to which substrate molecule is bound
Substrate usually is relatively small molecule
Enzyme is large protein molecule
Therefore substrate binds to specific area on the enzyme