Acidity changes proteinase activity

Fig. 6.16. (A) Changes in proteinase activity in extracts from cotyledons of germinated Phaseolus vulgaris. Enzyme activity measured by amino acid release from a casein solution incubated with cotyledon extract at pH 5.5. (B) Changes in protein nitrogen level (a) and free amino acid level (o) in cotyledons of germinated Phaseolus vulgaris. Based on Yomo and Srinivasen, 1973 [145]...

There are also changes in the rates of metabolism as red blood cells appear and aerobic processes intensify (Lasker and Theilacker, 1962 Laurence, 1975 Timeyko and Novikov, 1991) during the early phases of ontogenesis. Oxygen consumption increases, as do the number of mitochondria and their protein contents (Abramova and Vasilyeva, 1973 Ozemyuk, 1993). The adenyl nucleotide pool (ATP and ADP) decreases (Milman and Yurovitsky, 1973 Boulekbache, 1981), while the activity of cytochrome oxidase increases (Ozemyuk, 1993). The increased energy metabolism corresponds to a considerable extent with motor activity (Reznichenko, 1980). In the yolk sac, the activity of proteinase, which supplies nitrogenous materials to the embryo, increases, as does the rate of amino acid incorporation into the body proteins. 

Understanding how HLE inhibitors work and/or designing new inhibitors requires a model of HLE s active-site and an understanding of its mechanism of action. All serine proteinases share a similar catalytic region and mechanism of action but differ in several amino acids in the extended substrate-binding region. These changes are responsible for the specificity differences between HLE and other serine proteinases. In some cases analysis of the enzyme-inhibitor interactions has only been carried out with other related enzymes, and those results are referenced as appropriate. One closely related enzyme, porcine pancreatic elastase (PPE, EC 3.4.21.36) has... 

Mutations that result in amino acid substitution at the cleavage site in a protein substrate cause two changes in the proteolytic process. First, the rate of cleavage of the peptide bond is reduced because of the altered orientation of the substrate within the active site. Second, the altered substrate is very likely to be a competitive inhibitor of the proteinase responsible for the cleavage. Both of these effects are evident in the phenomenon called activated protein C resistance. 

Data are shown in Table 15.45 for white bread prepared with and without papain. There is a rise in the content of both free amino acids in the crumb and volatile carbonyl compounds in the crust when proteinase is used. As long as proteinases are active in a baking process, they release amino acids from flour proteins, which are then changed via Strecker degradation... 

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