What is true regarding gastrin ?
|A||It shows macroheterogeneity|
|B||It shows microheterogenity|
|C||It is mainly inactivated in the kidney and small intestine|
|D||It is formed from its precursor, preprogastrin|
A. Macroheterogeneity :
1. This general term refers to a polypeptide hormone that is secreted in different forms due to the difference in the number of amino acids in them . For example, gastrin is secreted in many forms (all these forms have the same carboxyl terminal configuration) :
2. G 14, G 17 and G 34 are the main forms (the number refers to the number of amino acid residues in the gastrin molecule); G 17 is the main form with respect to gastric acid secretion.
G 14 and G 17 : 2 to 3 minutes
G 34 : 15 minutes
a. One form has more than 45 amino acids
b. Another form is the carboxyl terminal tetrapeptide ( this has all the actions of gastrin; however, it is only 1/10th as potent as G 17)