Trypsin and trypsinogen

The oxidation of trypsin and trypsinogen was carried out in aqueous 0.1 M acetate buffer solutions at room temperature. In this particular case and under these conditions no significant cleavage of peptide bonds next to tryptophan residues occurred. Careful analysis of hydrolyzates of NBS-oxidized trypsinogen and trypsin confirmed the selectivity of the oxidative modification of the protein, as Table XXIV shows. There is no significant loss of tyrosine, histidine, serine, threonine, or cystine, although all of these amino acids will react with NBS but considerably less rapidly than tryptophan. 

C. Application Topographical Analysis of the Molecular Surfaces of the Proteins Trypsin and Trypsinogen... 

Linguistic Variabies in Moiecular Recognition 239 TABLE I Topographical Domains of Trypsin and Trypsinogen°... 

Vandlen and Tulinsky report a 3.5 A resolution comparison of the structure of a-chymotrypsin at pH 6.7 with that at pH 3.9, which shows that there has been a conformational change between these pH values. However, a comparison of the structures of native elastase at pH 5 and pH 8.S shows that, in both cases, the active-site histidine is hydrogen-bonded to Asp-102 and Ser-195 as found in a-chymotrypsin. The only difference appears to be the presence of two bound sulphates at pH S, one of which lies 6 A from the side-chains of His-57 and Ser-195. In a similar way there appears to be no conformational change in the crystals of DIP-inhibited trypsin between pH 5 and pH 9, although there are conformational chan in solution in both trypsin and trypsinogen between these values. 

For some enzymes, an inactive precursor called a zymogen is cleaved to form the active enzyme. Many proteolytic enzymes (proteases) of the stomach and pancreas are regulated in this way. Chymotrypsin and trypsin are initially synthesized as chymotrypsinogen and trypsinogen (Fig. 6-33). Specific cleavage causes conformational changes that expose the enzyme active site. Because this type of activation is irreversible, other... 

Fig. 6. Activation of chymotrypsinogen(s) and trypsinogen as a function of added trypsin (22). On the left chymotrypsinogen(s) activation in pig juice. Incubation time, 120 min. The other conditions are the same as in Fig. 5. On the right trypsinogen activation in pig juice. Incubation time, 18 hr. Abscissas, milligrams of added trypsin per 100 mg of total protein. Ordinates, specific activity (/i-equivalents/ min/mg of protein) after deduction of the activity of added trypsin.

It is evident that monochromatic rotations are a useful adjunct to any study of protein structure, but a final illustration of the insight that rotatory dispersion can provide may be seen in the conformational analysis of ehy-motrypsinogen activation. Neurath et al. (1956) have found an exact correlation between the rate of activation of both chymotrypsinogen and trypsinogen as measured by the enzymatic activity of their products and the rate at which their specific rotations become more positive, a change which Neurath and Dixon (1957) suggest represents an increase in helical content. By dispersion measurements on chymotrypsinogen and x-chymo-trypsin, Imahori et al. (1960) have demonstrated that a twofold increase in helical content, from 12 to 24 %, indeed occurs. They are thus able to esti-... 

Trypsinogen The calcium ion promotes the activation of trypsinogen to trypsin, and stabilizes trypsin under harsh conditions. 

The stability of the zymogens is rather fragile a very small amount of active trypsin can activate trypsinogen to create more trypsin and generate an autocatalytic reaction. Trypsin also activates the other zymogens. The normal pancreas protects itself from this catastrophe by a trypsin inhibitor, a small polypep-... 

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