Pepsin Pepsinogen

Pepsin Pepsinogen Stomach 42 amino acids HC1 and pepsin Amino group contributed by Tyr, Phe, Leu... 

The proteases are secreted as inactive zymogens the active site of the enzyme is masked by a small region of its peptide chain, which is removed by hydrolysis of a specific peptide bond. Pepsinogen is activated to pepsin by gastric acid and by activated pepsin (autocatalysis). In the small intestine, trypsinogen, the precursor of trypsin, is activated by enteropeptidase, which is secreted by the duodenal epithelial cells trypsin can then activate chymotrypsinogen to chymotrypsin, proelas-tase to elastase, procarboxypeptidase to carboxypepti-dase, and proaminopeptidase to aminopeptidase. 

Pepsinogen is produced by the chief cells. Within the lumen of the stomach, this precursor molecule is split by HCl to form the active enzyme pepsin. Optimally active at an acidic pH (pH = 2), pepsin begins protein digestion by fragmenting proteins into smaller peptide chains. 

The stomach secretes pepsinogens, which are inactive proteolytic enzymes, and protons - the high concentration of which initiates hydrolysis of the pepsinogens to form active pepsins, which then continue their own activation, via an autocatalytic, hydrolysis (Appendix 4.1). 

The hydrochloric acid in gastric juice is important for digestion. It activates pepsinogen to form pepsin (see below) and creates an optimal pH level for it to take effect. It also denatures food proteins so that they are more easily attacked by proteinases, and it kills micro-organisms. 

The self-activating process for converting an inactive catalyst, I, to its active form, A. Such processes typically display a discernible lag-phase followed by accelerated conversion of I to A. Zymogen activation can display autocatalysis, as exemplified by the conversion of pepsinogen to active pepsin at low pH. Many growth processes can also be described via an autocatalysis curve. 

CONTROL COEFFICIENT Convergence-point method, POINT-OF-INTERSECTION Conversion of pepsinogen to active pepsin, AUTOCATALYSIS Cooperative oxygen binding,... 

RIBULOSE-5-PHOSPHATE 3-EPIMERASE PEPSINS and PEPSINOGENS Peptide bond(s),... 

The activation of pepsin from its zymogen pepsinogen occurs by a different mechanism. In this case, the pH of the environment plays a decisive role. In the strongly acidic milieu of the stomach cleavage of a 44 amino acid peptide occurs from the inactive precursor pepsinogen. The activation is intramolecular and depends on the pH of the solution. 

Pepsin This acid-stable endopeptidase is secreted by the serous cells of the stomach as an inactive zymogen (or proenzyme), pepsinogen. In general, zymogens contain extra amino acids in... 

Pepsin is secreted as the inactive pepsinogen, which is activated by H+ ions at a pH below 5. Determination of its crystal structure revealed that in the proenzyme the N-terminal 44-residue peptide segment lies across the active site, blocking it.384 At low pH the salt bridges that stabilize the proenzyme are disrupted and the active site is opened up to substrates. 

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