Some small RNAs (ribosimes) have a similar function
Catalyze specific biochemical reactions
Almost every reaction in a living organism requires an enzyme
They organize, coordinate, regulate the cell metabolism
Why study enzymes
Genetic disorders: amount of enzyme; changes in the enzyme kinetics; abnormal enzyme
Drugs: enzymes, enzyme inhibitors
SNPs in the genes coding for certain enzymes – drug metabolism variations
Enzyme-based diagnostic tests in clinical practice
Diseases are diagnosed by the enzyme activities
Nutrition: enzyme deficiencies o nutritional deficiencies; personalized diets
General properties of enzymes
Increase the velocity of a spontaneous chemical reaction without being changed in the overall process; they change the reaction equally in both directions, and they do not change the equilibrium of the reaction
High catalytic activity
They function in solutions, at physiological pH, T and in negligible amounts
Highly specialized catalysts
Enzymes are highly specific
Reaction specificity: One and the same substrate o different enzymes o different products
Substrate specificity
General characteristics of enzymes
Active center: unique, three-dimensional
Regulated
Specific localization
Cell localization of enzymes
1. Cytosol: glycolysis, PPP, FA synthesis
2. Mitochondria: Krebs cycle, FA oxidation, decarboxylation of pyruvate
3. Lysosomes: degradation of biomolecules
4. Nucleus: DNA and RNA synthesis
Holoenzyme
Apoenzyme + non protein compound (cofactor)
Cofactors
Coenzymes
Prosthetic groups
Nomenclature
Trivial names
Suffix "-ase"
Nomenclature system of the International Union of Biochemistry and Molecular Biology (IUВMB)
Chemical elements that function as prosthetic groups in enzymes
Cofactors involved in proton and electron transfers
NAD(P)+
Flavine coenzymes: FMN, FAD
Lipoamid
Glutathione (GSH)
Ubiquinone
Ascorbic acid
Heme
Vitamins
Chemically unrelated organic compounds
They cannot be synthesized by humans, must be supplied by the diet
Needed in minor amounts
Required to perform specific cellular functions
They are precursors of coenzymes
Classified based on their solubility and functions
Vitamin C
Source: green vegetables, potatoes, rose hips, black current, tomatoes, peppers, citrus fruits
Deficiency: fragile blood vessels, scurvy in more severe deficiencies (deficiency in the hydroxylation of collagen, resulting in defective connective tissue)
Role – reducing agent: Coenzyme in hydroxylation reactions, facilitates the absorption of dietary iron, important antioxidant, maintains metal ions in reduced state, role in the catabolism of tyrosine
Vitamin C - clinical aspects
May have a role in the prevention of atherosclerosis and cancer
Role in immunity response
Vitamins complex B
Thiamine (В1)
Riboflavin (В2)
Niacin (В3)
Pantothenic acid (В5)
Pyridoxine (В6)
Biotin (B7)
Folic acid (B9)
Cobalamin (В12)
Thiamin (В1)
Biologically active form: thiamin pyrophosphate
Role: Coenzyme in the formation or degradation of α-ketols by transketolase (non-oxidative reactions of PPP) and in the oxidative decarboxylation of D-keto acids (pyruvate DH complex; D-KG DH complex)
Source: beans and wheat, meat, liver, yolk
Deficiency: Beriberi, Wernicke-Korsakoff syndrome
Riboflavin (В2)
Biologically active forms: FMN, FAD
Role: Coenzyme in oxidation and reduction reactions, prosthetetic group of flavoproteins
Source: grains, milk, meat, eggs
Deficiency: Riboflavin deficiency (cheilosis, glossitis, and seborrheic dermatitis) is not associated with a major human disease, although it frequently accompanies other vitamin deficiencies