Metabolic fuels and Dietary components Lecture - 4 By Dr. Abdulrahman Al-Ajlan

Enzymes :  Enzymes are proteins that catalyze biochemical reactions, increasing their rates as much as a million times. The reactions of the cell would not occur rapidly enough to sustain life if enzyme catalysts were not present.

 The binding of the substrate to the enzyme is not random, but occurs at a specific active (or catalytic) site. Active sites of enzymes are the regions where substrates bind, are converted to products and released.

General properties of enzymes 1.Enzymes are not neither consumed during the reaction, nor produced during the course of a reaction. 2.Substrates bind at the active sites of enzymes where they are converted to products are released. 3.Enzymes are usually highly specific and produce only the expected products from the given reactions.

4.Many enzymes recognize only a single compound as a substrate. 5.Some enzymes such as those involved in digestion are less specific. 6.Many enzymes require cofactors that frequently are metal ions or derivatives of vitamins.

Enzyme Activity The activity of an enzyme is expressed in units. One international unit (IU) is the quantity of enzyme that will catalyze the reaction of one μmol of substrate per minute.

Classes of Enzymes Enzymes may be classified according to composition of the active enzyme or the type of reactions they catalyse. According to the composition, enzymes can be classified as.

Continue 1-Simple- protein structure alone is sufficient for catalytic activity (e.g. trypsin, chymotrypsin, elastase). 2- Complex-enzyme requires additional non-protein cofactors for full catalytic activity.

Continue  A complete catalytically active enzyme together with its cofactors is known as a holoenzyme. Cofactors may be organic in nature (coenzymes) or metal ions, and are involved in group transfer reactions. Most cofactors are linked to enzymes by non covalent bonds.

Catalytic efficiency Most enzyme catalyzed reactions are highly efficient, proceeding from10 3 to 10 8 times faster than uncatalyzed reactions. Each enzyme molecule is capable of transforming 100 to 1000 substrate molecules into product each second. The number of molecules of substrate converted to product per enzyme molecule per second is called the turnover number.

Regulation  Enzyme activity can be regulated, mean enzymes can be activated or inhibited, so, that the rate of product formation responds to the needs of the cell

1.substrate concentration When all the enzyme con, pH, T and electrolyte composition in solution are kept constant, the rate of an enzyme catalyzed increases until a maximum Velocity (V max ) is reached (a hyperbolic curve).The rate or velocity of a reaction (v) is the number of substrate molecules converted to product per unit time (μmoles product formed per minute). Factors affecting the rate of an enzyme catalyzed reaction

2.If the enzyme con is constant, the velocity increases with the substrate con until the maximum velocity, V max is attained. The maximum velocity is attained when all the active sites of the enzymes are saturated with substrate.

3.The velocity of a reaction increases with T until a maximum is reached, after which the velocity decreases. The decrease at high T is due to denaturation of enzyme. 4.Each enzyme has an optimum pH, that brings the best charges are present on both the enzyme and the substrate, resulting the velocity is at a maximum. Increases or decreases in the pH may alter these charges, so that, the reaction becomes at a slower rate. If the pH is too high or too low, the enzyme may also undergo denaturation