The reason is, as acidosis advances, most of the enzymes in our body become inefficient and eventually all chemical reactions

glucose molecules are subsequently absorbed by the portal blood. After being absorbed the glucose molecules may be catabolized into C02 and H20. During its catabolism large amount of energy is produced, but only a part of this energy appears as heat; rest of the energy is stored in the form of energy rich phosphate compounds like ATP (adenosine triphos-phate). ATP subsequently will supply energy for doing various works in the body (like, muscular contraction, chemical reactions etc. ). One of the aims of the catabolism, therefore, is to produce energy rich compounds. On the other hand glucose molecules may be broken down into simpler molecules, like pyruvic acid, CHS COCOOH; pyruvic acid may be aminated to form alanine. Alanine will subsequently be required for building polypeptides. The polypeptides in turn are required for production of the proteins ofthe body (e.g. , muscle), peptide hormones (e.g. , insulin) etc. The pyruvic acid may be further broken down to the two carbon structure, viz, acetic acid or rather 'active acetate' (acetyl coenzyme A, CH3 COSCoA) and required for synthesis of long chain fatty acids (e .g. palmitic acid) or cholesterol. Or, the glucose molecule may be requisitioned for the synthesis of glycogen. All these are examples of anabolism of glucose . ENZYMESDefinition. Special features of enzymic actions. Factors influencing enzymic activities. Mechanism of the actions of enzymes. Mechanism of inhibition of enzymic Classification Coenzyme, cofactor and prosthetic group. Isoenzymes. Regulatory enzymes. Applied physiology. Definition Enzymes are organic catalytic agents, protei in nature, produced by living cells but for whose actions presence of living cells are not necessary. Special features of enzymic (enzymatic) activity 1. Enzymes accomplish their action at body temperature, without harming the host cells Thus, oxidation, reduction or hydrolytic reactions, if done in the laboratory, will require great deal of heating, addition of corrosive quantities of acids or alkalis and yet long time. But within our body, the enzymes accomplish hydrolysis, oxidation, reduction etc, (i) at body temperature (38°C), (ii) without injuring the cells and (iii) speedily. Moreover, chemical reactions in the laboratory usually produce side products. Enzymic (enzymatic, ) catalysis does not produce side products. Thus, stated simply, enzymic catalysis is much more efficient process than man made catalysts. 2. Enzymes are highly specific. Thus, sucrase splits sucrose but not maltose, although sucrose and maltose molecules are closely similar. On the otherhand, maltase splits maltose but not sucrose. Some enzymes however can act on a group of chemically very closely related substrates (substrate = the chemical compound on which the enzyme acts. Thus sucrose is the substrate of the enzyme sucrase). Furthermore, the enzymes show optical specificity. Thus, the enzymes in our body which can act on L ammo acids, cannot act on D ammo acids. FACTORS INFLUENCING ENZYME ACTIVITIES I. Temperature Most of the enzymes in our body act best around our normal body temperature, say around 38°C. If the temperature of the reaction medium falls, the efficiency of the enzyme also falls. At around 0°C, the enzymes become remarkably inactive and become totally inactive at around - 20°C. But on thawing the activity reappears in the enzyme. If the medium in which the enzyme is acting, becomes too hot, the enzyme, being protein in nature, is denatured. On further rise of temperature, the enzyme coagulates (heat coagulation). Cooling the enzyme now will not bring the activity of the enzyme back and the enzyme is said to be killed (by the heat). Optimal temperature is that temperature at which the enzyme acts best. Most human body enzymes are denatured if the temperature goes above 45°C. Plant enzymes, however, usually can survive somewhat higher temperatures. Fig. 7.1.1. Interrelationship between the temperature and enzyme activity. 2. Ph Every enzyme has an optimal pH, that is, a pH in which it acts best. Thus the optimal pH for pepsin, trypsin and salivary amylase, three digestive tract enzymes, are 1.5, 8.0, and 6.8 respectively. For probable explanation so as to how the pH influences the enzymic action, see mechanism of enzyme action, later this chapter. Outside its optimal pH, the enzyme loses its efficiency. Thus, in the stomach (where the pH is very low), there is a lipase, but as this lipase can act only in much higher pH, gastric lipase is an useless enzyme within the stomach of man. Or it is well known that acidosis is dangerous and if not corrected, leads to death. The reason is, as acidosis advances, most of the enzymes in our body become inefficient and eventually all chemical reactions (including the vital ones in the brain and heart muscle) stop and death ensues. 3. Effects of ions Some enzyme actions cannot proceed at all unless ions like Mg ++, Zn++ or Mn++ ions are present in the reaction medium. Cl- ions enhance the action of salivary amylase. 4. Concentration of the substrate As the concentration of the substrate on which the enzyme is acting rises, the velocity of the reaction increases, until a maximal velocity is obtained (V in fig. 7.1.2). Further increase of the substrate (without increasing the amount of the enzyme) does not cause increase of the rate of reaction (fig. 7.1.2). See also mechanism of enzymic action for explanation. Fig. 7.1.2. Effect of concentration of substrate on the velocity of reaction. MECHANISM OF ENZYME ACTION The enzyme combines