Chemistry of Enzymes Subscribe
Date: 31. October 2017
Introduction to Enzymes
Catalysts of biological systems-colloidal, thermolabile and protein in nature. Remarkable molecular devices that determine the pattern of chemical transformation and mediate the transformation of different forms of energy. Catalytic Activity of Enzymes are Immense catalytic power, accelerate reactions at least a million times, and Reduces the energy of activation
activation energy is a term coined by the Swedish scientist, Svante Arrhenius in 1889. It means the amount of energy expressed in joules that is required to convert the molecules in one mole of a reactant from a ground state to the transition state. Protein Nature of Enzymes involves Simple Enzymes and Conjugated Enzymes.
Types of Simple Enzymes are Monomeric enzymes: Ribonuclease, Oligomeric enzymes: Lactate dehydrogenase and Multienzyme complex: Pyruvate dehydrogenase.
Classification of Co-Enzymes
Co-enzymes are a specific, thermostable, low mol. Wt., non-protein organic substance usually derived as physiologically active forms from the constituents of vitamin B-complex. They are Also called as co-substrate or second substrate. They have Prosthetic Group: Covalently bonded coenzyme and Oxidoreductions, group transfers, Isomerization and covalent bond formation.
Classification of Co-Enzymes: For Transfer of Groups other than Hydrogen (they Include Sugar phosphates, coash, Thiamine pyrophosphate (TPP), Pyridoxal phosphate, Folate coenzymes and Biotin), For Transfer of Hydrogen (NAD+, NADP+ FMN, FAD, Lipoic acid, and Coenzyme Q) and Heme Acts as Coenzyme. The activity of many enzymes depends on the presence of certain metal ions such as K+, Mg++, Ca++, Zn++, Cu++.
Role of Metal Ions in Enzymes is that they help in either maintaining or producing (or both), active structural conformation of the enzymes and Formation of enzyme-substrate complex.
Types of Metal Ions in Enzymes are Metal activated Enzymes: In certain enzymes the metals form a loose and easily dissociable complex. The metal ions can be removed by dialysis or any other such method from the enzyme without causing any denaturation of apoenzyme, and Metalloenzymes: In this case metal ion is bound tightly to the enzyme and is not dissociated even after several extensive steps of purification.
Autocatalysis. A few enzymes exist in their inactive forms and are called as proenzymes or zymogens. Pepsin has Pepsinogen as its zymogen. The zymogens become active after undergoing some prior modification in its structure by certain agents. International Union of Biochemistry (IUB) adopted a nomenclature system based on chemical reaction type and reaction mechanism.
Classification of Enzymes
Classification of Enzymes are:
- Oxidoreductase are the Enzymes involved in oxidations and reductions of their substrates, For example Alcohol dehydrogenase, Xanthine oxidase and Glutathione reductase
- Transferases are the Enzymes that catalyze transfer of a particular group from one substrate to another, for example Aspartate and alanine transaminase (AST/ALT) and Hexokinase
- Hydrolases are the Enzymes that bring about hydrolysis, for example Glucose-6-phosphatase, Pepsin and Trypsin
- Lyases are the enzymes that facilitate removal of small molecule from a large substrate for example Fumarase, Arginosuccinase and Histidine decarboxylase
- Isomerases, Enzymes involved in isomerization of substrate for example DP-glucose, Epimerase, Retinal isomerase, Racemases and Triosephosphate isomerase
- Ligases, Enzymes involved in joining together two substrates: Alanyl-t. RNA synthetase, Lutamine synthetase, DNA ligases
Properties of Enzymes
Models of Enzyme-Substrate Complex are
- Template or Lock-and-Key Model that is Originally proposed by Fischer. The active site by itself provides a rigid, pre-shaped template fitting with the size and shape of the substrate molecule
- Induced-Fit or Koshland Model, Proposed by Koshland in 1963, tells Flexibility of the region of active site
- Factors Affecting Enzymes Action are Temperature, pH, Enzyme Concentration, Product concentration, Substrate concentration, Activators and Coenzymes, and time, all of these factors are explained in detail with diagrams
Inhibition and Control of Enzymes
inhibitors and the process is called as enzyme inhibition. Inhibitors are sometimes referred to as negative modifier. They may be small inorganic ions, or organic substances. Then Competitive & Non-Competitive Inhibition and Allosteric Enzymes are illustrated with diagrams.
Feedback Regulation vs Feedback Inhibition: In both mammalian and bacterial cells, end-products “feedback” and control their own synthesis. In many instances, this involves feedback inhibition of an early biosynthetic enzyme. Dietary cholesterol restricts the synthesis of cholesterol from acetate in mammalian tissues. This is feedback regulation. This feedback regulation, however, does not appear to involve “feedback inhibition” of an early enzyme of cholesterol biosynthesis.
Control of Enzyme Degradation was discovered by Aaron Ciechanover, A Hershko and Irwin Roose who got Nobel Prize.
Ubiquitin is a small, approximately 7s residue protein that is highly conserved among eukaryotes. Ubiquitination is catalyzed by a large family of enzymes called “E3 Ligases”, which attach ubiquitin to the side chain amino group of lysyl residues. Uses of Enzymes are Enzymes estimation in serum and body fluids for diagnosis and prognosis, Enzyme used as laboratory reagent, and Therapeutic uses of enzymes.