before it is trapped in Ihe liver and converted to urea, the NH3 coming from the intestine moves via the portal venous blood.

become glulamic acid, alanipe or aspartic acid respectively. The glulamic acid is subsequently again deaminated as shown below. [As there is a concomitant oxidation, the process is an example of oxidative deamination (see below)]. How glulamic acid becomes a keloglutaric acid again Now, Ihe a keloglutaric acid is again available as a recipient. The enzyme, glulamate dehydrogenase, is present in most of the tissues. As a typical example of transamination, the reaction involving aspartic acid and a keloglutaric acid (equation involving structural formule shown overleaf) may be cried The reaction is calalyzed by the transaminase, called glutamate-oxaloacetate transaminase (GOT), (also called 'asparate aminolransferase'). Normally, human serum contains a small amount of this (GOT) enzyme. The value of this serum glulamate oxaloacetate transminase (SGOT) rises after myocardial infarction, or gross liver damage (which may be due to acute viral hepatitis) or even after massive skelelal muscle damage. This is because, in all such tissues, GOT is presen mtracellularly, and are released from them following their damage. Thus, like ECG findings, a high rise of SCOT in a case, suspected to have developed myocardial infarction, confirms the clinical diagnosis. [At this stage, the student may try to figure out the whole picture : the amino add aspartic add □ amino group removed so that oxaloacetic arid, OAA and glutamic add formed. OAA enters Krebs cycle while glutamic add loses NH2 to form a ketoglutaric add again. The NH2 group goes to form urea). The lansmination reaction is the most important of all the reactions aimed to remove NH2 group from an aminoacid. All transaminase syslems ( enzymes effecting Ihe transamination) contain pyridoxal phosphate, which plays an important role in the reaction as a coenzyme. The major site of transamination is liver. Deamination Qxidativedeamination As shown below, the enzyme concerned is called Lamino acid oxidase. L-amino add oxidase is found mainly in the liver and kidney. It is, it appears, is not a major path for removal of NH2 group from most of the amino acids Three amino acids, viz, threonine, cysteine and serine are deaminated by this process As an example, the deamination of cysteine is shown above. By this reaction formation of ammonia, as shown above, occurs. N. B. The term 'deamination' is used by some authors to mean oxidative and non oxidative deamination as well as transamination. Other authors, however, do not transamination in the category of deamination The deamination of glulamic acid by glutamic dehydrogenase is also an example of oxidative deamination. Animation of keto acids Many keto acids in our body can catch NH2 group from an amino acid and as a result is converted into the corresponding amino acid. As an example, pyruvic acid (CH3C 0 COOH) can be converted into alanine, (CH3CHNH2 COOH). In this way some (but not all) amino acids can be synthesized in our body, provided that the raw materials (i.e , the corresponding keto acid and the NH2 group) are available. Transamination is a process by which such catching of NH2 group can occur. There are ten amino acids which cannot be synthesized in our body Such amino acids, therefore, have to be present in the food and are called essential amino acids (for details, see chapter on nutrition, chap. 16, sec. VII). Thus, as shown above, alanine cannot be an essential amino acid. Ammonia formation and removal (a) Sources of ammonia Glulamic acid dehydrogenase is present in majority of the tissues of our body As shown above, glutamic acid dehydrogenase acts on the glutamic acid to produce a ke-toglutaric acid and aminonia (NH3). The baclerial flora of the intestine also produces. NH3. This is produced by either of the two ways: the urea of the intestinal juice (urea is present in all body fluids) is acted upon and split by the baclerial en zymes and as a result NH3 is produced; the bacterial enzymes may attack the food proteins and form NH3. The NH3 produced in the intestine goes to the liver via portal vein. Kidneys also can produce ammonia (for details, chap 8.2). Removal of the ammonia The liver converts the NH3 into urea, and thus the NH3 is eliminated; NH3 is very toxic while the urea is no Obviously, before it is trapped in Ihe liver and converted to urea, the NH3 coming from the intestine moves via the portal venous blood. The blood ammonia concentration of systemic circulation is normally about 40ugms/100 m1. Excessive blood ammonia concentration causes damage of the brain. In liver failure (hepalic coma) the blood NH3 concentration, therefore, rises □ patient develops coma and death occurs as a result. Glutamine can be split in the kidney by glutaminase into glutamic acid and ammonia and the glutamic acid is thus regenerated. The ammonia is converted into occurs and this is how brain can combat with an excess blood ammonia level to some exlent. This forms Ihe basis of treatment by glutamate in hepatic coma lo combat with excess ammonia. In severe liver damage, therefore, one of the major lines of treatment is to reduce or stop ammonia formation by intestinal bacteria, this is done by using antibiotics (to deslroy the intestinal bacterial flora) and by drastic reduction of food prolein. Otherwise accumulation of NH3 occurs because the liver fails to remove it. UREA SYNTHESIS Site Urea synthesis occurs in the liver. Urea is mainly excreted as urinary urea via the kidney. Mann showed that in experimental animals, if the liver is removed (keeping the kidneys intact) the bloo