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Pepsin remains in the larynx following a gastric reflux event. [16] [17] At the mean pH of the laryngopharynx (pH = 6.8) pepsin would be inactive but could be reactivated upon subsequent acid reflux events resulting in damage to local tissues. Pepsin exhibits a broad cleavage specificity. Pepsin will digest up to 20% of ingested amide bonds. [18]
All have an optimum pH. The pH can stop enzyme activity by denaturating (altering) the three-dimensional shape of the enzyme by breaking ionic, and hydrogen bonds. Most enzymes function between a pH of 6 and 8; however pepsin in the stomach works best at a pH of 2 and trypsin at a pH of 8.
The optimum pH for its action is approximately 7. [10] Its concentration does not correlate with the amount of HCl or pepsin in the gastric juice, e.g., intrinsic factor may be present even when pepsin is largely absent. [11] The site of formation of the intrinsic factor varies in different species.
The values below are standard apparent reduction potentials (E°') for electro-biochemical half-reactions measured at 25 °C, 1 atmosphere and a pH of 7 in aqueous solution. [ 1 ] [ 2 ] The actual physiological potential depends on the ratio of the reduced ( Red ) and oxidized ( Ox ) forms according to the Nernst equation and the thermal voltage .
Studies of proteins adapted to low pH have revealed a few general mechanisms by which proteins can achieve acid stability. In most acid stable proteins (such as pepsin and the soxF protein from Sulfolobus acidocaldarius), there is an overabundance of acidic residues which minimizes low pH destabilization induced by a buildup of positive charge ...
The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). [1] However, pI is also used. [2] For brevity, this article uses pI.
The optimum pH for the group of enzymes is around pH 8, but some individual enzymes within this group may be distinguished by their differences in stability and optimum pH. [ 5 ] References
In general, they have two highly conserved aspartates in the active site and are optimally active at acidic pH. Nearly all known aspartyl proteases are inhibited by pepstatin. [1] Aspartic endopeptidases EC 3.4.23. of vertebrate, fungal and retroviral origin have been characterised. [2]