Enzymes

Characteristics All Enzymes are Proteins Catalysts – i.e. control the rate of a chemical reaction

How Enzymes work Enzymes bind and hold substrates (aka reactants) in a certain orientation to speed the chemical reaction along Enzymes change shape as they bind the substrates

the binding substrates + enzyme-substrate complex active site

the reaction, the release enzyme-substrate complex product

What about the other way? substrate enzyme-substrate complex enzyme product

Lactase 1926 aa’s long cell membranes - small intestines Lactase

Beano - alpha galactosidase breaks down trisaccharides raffinose – in beans, cabbage enzyme not in humans in bacteria in large intestines Raffinose is a trisaccharide composed of galactose, fructose, and glucose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose can be hydrolyzed to D-galactose and sucrose by the enzyme α-galactosidase (α-GAL), an enzyme not found in the human digestive tract. Humans and other monogastric animals (pigs and poultry) do not possess the α-GAL enzyme to break down RFOs and these oligosaccharides pass undigested through the stomach and upper intestine. In the lower intestine, they are fermented by gas-producing bacteria which do possess the α-GAL enzyme and make carbon dioxide, methane, and/or hydrogen—leading to the flatulence commonly associated with eating beans and other vegetables. α-GAL is present in digestive aids such as the product Beano. Beano is a product containing the enzyme alpha galactosidase, which is derived from the fungus Aspergillus niger. +

another example – glyceraldehyde-3-dehydrogenase

re-introducing activation energy activation energy is the energy required to get a reaction going activation energy net energy change

How do Enzymes work? They lower the “activation energy” of the reaction activation energy is the energy required to get a reaction going activation energy net energy change

How do they do it? They lower the “activation energy” of the reaction net energy change

Enzyme performance is affected by: amount of substrate present temperature pH Inhibitors Poisons

Enzymes and Amount of Reactants [ reactants ]  reaction rate because increased chance of finding molecules [reactants]  reaction rate because decreased chance of finding molecules 1. Measure [S] or [P] 2. Combine and Plot Experiment with amount and rate

Enzymes and Temperature temperature  reaction rate because increased kinetic energy breaks H-bonds temperature  reaction rate because decreased kinetic energy does not break H-bonds

pH Acids – excess Hydrogen ions Bases – excess hydroxyl ions Neutral – equal numbers of H+ and OH-

Enzymes and pH pH changes reaction rate because H-bonds are altered Experiment with pH and rate

Enzymes and pH each enzyme has an optimal pH; some work best in acidic conditions (<4) (pepsin) while others work best closer to a neutral pH (7) pH for Optimum Activity Enzyme pH Optimum Lipase (pancreas) 8.0 Lipase (stomach) 4.0 - 5.0 Lipase (castor oil) 4.7 Pepsin 1.5 - 1.6 Trypsin 7.8 - 8.7 Urease 7.0 Invertase 4.5 Maltase 6.1 - 6.8 Amylase (pancreas) 6.7 - 7.0 Amylase (malt) 4.6 - 5.2 Catalase 7.0

Enzymes and Inhibitors

Enzymes and Inhibitors bind to specific enzymes and decrease the reaction rate Normal substrate enzyme binding Competitive inhibitor binds to the active site Noncompetitive inhibitor binds to the enzyme and changes its shape

Competitive Inhibitors

Noncompetitive Inhibitors A noncompetitive inhibitor is a substance that interacts with the enyzme, but usually not at the active site. The noncompetitive inhibitor reacts either remote from or very close to the active site. The net effect of a non competitive inhibitor is to change the shape of the enzyme and thus the active site, so that the substrate can no longer interact with the enzyme to give a reaction. Non competitive inhibitors are usually reversible, but are not influenced by concentrations of the substrate as is the case for a reversible competive inhibitor. See the graphic on the left. Irreversible Inhibitors form strong covalent bonds with an enzyme. These inhibitors may act at, near, or remote from the active site. Consequently, they may not be displaced by the addition of excess substrate. In any case, the basic structure of the enzyme is modified to the degree that it ceases to work. Since many enzymes contain sulfhydral (-SH), alcohol, or acid groups as part of their active sites, any chemical which can react with them acts as an irreversible inhibitor. Heavy metals such as Ag+, Hg2+, Pb2+ have strong affinities for -SH groups. Nerve gases such as diisopropylfluorophosphate (DFP) inhibit the active site of acetylcholine esterase by reacting with the hydroxyl group of serine to make an ester. Oxalic and citric acid inhibit blood clotting by forming complexes with calcium ions necessary for the enzyme metal ion activator.

Poisons - KCN Specific Irreversible Inhibitor of Cytochrome C Oxidase, ATP cannot be made Anaerobic respiration only Fatal build up - Lactic Acid

Poisons - Arsenic Nonspecific Inhibitor of cellular respiration enzymes Inhibits glucose break down Cell death results