Enzymes are catalytic proteins in living systems. Reactions in living cells, which occurs very quickly at an approximate neutral pH and body temperature, can occurs due to the presence of enzymes. Enzymes are synthesized in cells, many enzymes can extracted from cells without losing its activity. Enzymes work very specifically. An enzyme can only catalyze several reactions, often only one type of reaction. Enzyme specificity These can be differentiated based on optical and cluster specificities. 1. Factors that influence the speed of enzyme reactions. Changes in pH and temperature have a big effect on enzyme work. Concentration enzyme, substrate, and electrolyte concentrations as well as the presence of activators, inhibitors and coenzymes, under certain circumstances are an important factor. Reaction results Enzymes can also inhibit the work or speed of enzyme reactions. a. Effect of Temperature Low temperatures near freezing usually do not damage the enzyme. At the temperature when the enzyme is still active, an increase in temperature of 100 C causes activity the enzyme becomes twice as large (Q10 = 2). The reaction takes place most quickly at the optimum temperature. The optimum temperature for enzymes in the human body is around 370 C. The enzymes of microorganisms that live in high temperature environments have a temperature higher optimum. If the temperature continues to be increased, the number of active enzymes will decrease because undergoes denaturation. Most enzymes become inactive when heated to a temperature of 60C. Under some circumstances, if heating is stopped and the enzyme is cooled again, its activity is restored. This happens because the denaturation is still reversible. The pH value and the presence of protective substances can be influence the denaturation caused by this heating. b. Effect of pH Measurements at different pHs show that the activity is optimal Most enzymes in the body occur at a pH between 5-9, except for a few enzymes such as pepsin (optimum pH 2). This is caused: 1. At very low or high pH, the enzyme will be denatured. 2. At low or high pH, enzymes or substrates can experience changes in charge so that the activity changes c. Effect of Enzyme Concentration The enzyme reaction speed (V) is directly proportional to the enzyme concentration (E). The greater the number of enzymes, the faster the reaction In an enzyme reaction, the enzyme molecule binds to the substrate (S) to form enzyme-substrate complex (ES). This complex is then broken down into yields reaction (P) and free enzyme (E). d. Effect of Substrate Concentration If the substrate concentration [S] increases, while other conditions remain constant, then the enzyme reaction speed also increases to the maximum limit (Vmax), namely when the enzyme is saturated with the substrate. At points A and B, not all enzymes have reacted with the substrate so the addition of S will increase the amount of ES and the enzyme reaction speed (V) according to the addition of S. At point C, all enzymes have reacted with S so the addition of S will not increase the speed of the enzyme reaction because no more free enzymes. At point B, the enzyme reaction speed is exactly at half (1⁄2) maximum speed. Yielding substrate concentration half (1⁄2) maximum speed is called Km or Michaelis constant. e. Effects of Oxidation The sulfhydryl group (-SH) of an enzyme is essential for its activity. If This group is oxidized, then a disulfide bond (SS) is formed which causes enzyme activity is lost. Oxidation can be caused by air oxygen or by other oxidizing agents. Sometimes enzymes can become active again if additions are made certain reducing agents such as glutathione or cysteine (R-SH). This reducer converts disulfide bonds back into sufhydryl groups. f. Influence of Other Factors Enzymes can be damaged by shaking or irradiation with alpha UV light, beta, and gamma. Irradiation causes the formation of peroxide then oxidizes the active group of the enzyme. 2. Coenzyme. Many enzymes can only work in the presence of non-protein organic molecules certain substances are called coenzymes. The complete system of enzymes and coenzymes is called holoenzyme, while the protein part alone is called apoenzyme. So: Apoenzyme + Coenzyme = Holoenzyme B complex vitamins are generally part of the structure coenzyme.Vitamin B6, for example, is required for amino acid metabolism; nicotinamide, thiamine (B1), riboflavin (B2), pantothenic acid and folic acid required for biological oxidation reactions. Folic acid is also needed for metabolism of substances with one carbon atom.