483 Lecture 4 - Glutamate Oxaloacetic Acid Transaminase (GOT) Purification -- Expt 3 Part A
2. GOT Physiological Function
Transaminases are involved in the cell in the formation of amino acids for which the cell can synthesize the 2-keto-acid. There are many different transaminases in the cell which basically differ only in substrate specificity. So you may find it very interesting that there are actually 2 forms of GOT in the typical mammalian cell such as those like the pig heart we are extracting the GOT from in this expt. Why are there iso-enzymes of GOT in the cell? (iso-enzyme means that there are 2 or more enzymes with the same substrate specificity but differ in amino acid sequence and in cell location). The existence of GOT iso-enzyme forms has to do with the cellular function of GOT being involved carbon compound transport:
This graphic illustrates the role of the 2 forms of GOT, one in the mitochondria and one in the cytosol. The pathway shown is for synthesis of sugar (glucose) to replenish and keep your blood sugar at a normal level when there has been no recent intake of carbohydrates in your food. The pathway is called gluconeogenesis (see Fig. 10-3 in text). Here the mitochondrial GOT runs in the direction were are assaying it this lab, while the cytoplasmic GOT runs in the opposite direction to provide OAA (oxaloacetate) for synthesis of PEP (phosphoenolpyruvate) in the cytoplasm. PEP is the key intermediate for the synthesis of glucose, which can be exported to the blood from liver or heart cells. The origin of pyruvate in the mitochondrion is most likely amino acids resulting from the breakdown of proteins during fasting or between carbohydrate containing meals.
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