Enzyme aging

Reactivators of phosphorylated ChE. Pyridine aldoxime methiodide (PAM) and related compounds are the best known. They reactivate the phosphorylated enzyme so long as aging has not occurred. They do not, however, reactivate the aged enzyme. ChE which has been phosphorylated by certain nerve gases ages rapidly ... 

It is also important to mention the use of the reactivation of the acetylcholinesterase by pyridine-2-aldoxime methochloride to discriminate between the toxin and potential insecticides [96]. Once phos-phorylated, the active site serine of the enzyme can be reactivated by powerful nucleophilic agents such as oximes. However, this reactivation is not possible if attempted too late due to the stable adduct formed by the dealkylation (aging) of the inhibitor s remaining group. When acetylcholinesterase is inhibited by anatoxin-a(s), it shows immediately the characteristics of an aged enzyme and cannot be reactivated. In this way, it is possible to distinguish between the inhibition caused by anatoxin-a(s) and the one provoked by other insecticides. 

Reactivation of alkylphosphorylated acetylcholinesterase. Spontaneous reactivation (dashed arrow) by water occurs at an insignificant rate however, loss of one isopropoxy group occurs at a much more rapid rate, yielding the aged enzyme, which is resistant to reactivation. The regeneration of the enzyme by pralidoxime is shown at bottom. 

Enzymes are proteins. They are sensitive to denaturation by pH, temperature, or aging. Enzymes have an optimal pH range in which their activity is maximal this pH range should be compatible with the transducer. Moreover, most of the biological systems have a very narrow range of temperature (15-40 C). The most important problem and main drawback for industrial exploitation is the short lifetime associated with the biological elements. 

Fig. 5. The appearance of enzyme activity and response to hydrocortisone mediated induction of cysteine dioxygenase, and the change of cysteine contents in rat liver during development. Rats were injected with hydrocortisone acetate(0.1 mg/g body weight) 25h, 20h, 15h, lOh prior to sacrifice at 2 or 4-, 8-, 12-, and over 16-postnatal-day respectively, since the time reaching the maximum induction is differ from each other depending on the age. Enzyme activity with (0) Of without(O) hydrocortisone injection. Cysteine contents in rat liver (A) Results are expressed as the mean S.D.(represent by vertical line) of five animals.

Flours are commonly treated with additives and enrichment premixes to standardize quality and meet regulations. The treatments commonly consist of flour bleaching, maturing or aging, enzyme supplementation, and addition of the enrichment to supplement selected minerals and vitamins. Hard wheat flours are, in some instances, oxidized with azodicarbonamide, ascorbic acid and/or, in some countries, with potassium bromate in order to improve functionality. Soft wheat flours are in some instances chlorinated to produce bleached cake flours. The normal range of chlorination ranges... 

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