The Digestive Enzyme

This physiological mechanism is negociate through parasympathetic pathways fit(p) in the vagus spunk (2:419). In the presence of acidic pH, pepsinogen undergoes a multistage activation process, or "autocatalysis." Intramolecular cleavage by the pepsin active site converts the pepsinogen to proteolytic pepsin. This transformation essentially involves splitting astir(predicate) nine peptide bonds. in that location is a loss of a variable number of aminic acids from the N terminal sequence. This reduces pepsinogen's molecular weight of 43,000 by closely 5,000 molecular weight (4:743-750). Ultimately, the gastric proteases consist of a undivided polypeptide chain turn outing three intramolecular disulfide bridges (3:57). Upon activation, this chain undergoes pass on conformational alteration (5:1-7). Pepsin is essentially a bilobal molecule. Its devil domains are uninvolved by a deep cleft lying orthogonal to the molecule's largest diameter. Zymogen activation is thought to expose active sites located within this cleft (3:61).

Bergman (1942) divided the proteolytic digestive enzymes into two classes. These consisted of the exo-peptidases and the endo-peptidases. Pepsin is an endo-peptidase. It cleaves peptide bonds within proteins and polypeptides (8:667). Moreover, although the enzyme acts on a wide variety of substrates, its proteolytic activity, does not take place indiscriminately. Pepsin has a distinct orientation course for the peptide

1. Allen, A.; Pearson, J. P.; Blackburn, A.; Coan, R. M.; Hutton, D. A.; Mall, A. S. Pepsins and the mucus barrier in peptic ulcer disease. Scandinavian Journal of Gastroenterology. Supplement. 146:50-57; 1988.

One pathophysiologic chore associated with abnormal pepsin functioning is peptic ulcer. As far tail as 1932, Vanzant et al. observed a relationship between pepsin discrimination and the severity of ulcer disease. Moreover, the hypothesis received further choke from detailed studies performed in 1963 by Borg and Bergstrom (9:233-238). Although the cause of chronic peptic ulceration is not yet known, researchers do agree that it results from an derangement between "aggressive" and "defensive" factors.

The stomach's protective mucus cladding is continuously eroded by luminal pepsin. Gastric ulceration may result when this erosion becomes excessive.

8. Smyth, D. H. The intake of materials--nutrition, metabolism. In Davson, H.; Eggleton, M. G., eds. Starling and Lovatt Evans principles of pitying physiology. Thirteenth edition. Philadelphia, PA: Lea & Febiger, 1962; pp. 447-685.

In addition to electrophoretic and immunologic variability, the pepsinogens also display remarkable brokertic heterogeneity. For example, about 15% of Caucasians do not produce Pg5. This deficiency, known as "phenotype B," is inherited as an autosomal recessive trait. Researchers using cDNA probes have determined that this unusual genetic polymorphism is, not due to multiple alleles at a single gene locus, but rather results from the occurrence of multiple genes. A entangled containing variable numbers of pepsinogen I genes has been identified on humankind chromosome 11. The observed polymorphisms are caused by 3 different haplotypes which contain both 3, 2, and 1 genes, respectively. For example, the haplotype with 3 genes contains PGA5, PGA4, and PGA3. In contrast, the haplotypes for phenotype B, contain either 2 and 1 genes: the 2 gene haplotype comprises PGA4
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