Enzymatic Hydrolysis of Native Proteins

Examination of the action of proteolytic enzymes on native proteins (or biologically active peptides) can yield two important types of information. First, determination of the susceptibility of particular bonds in a protein substrate offers a means for evaluation of certain features of the conformation of the protein (Linderstr0m-Lang, 1952 Mihalyi and Harrington, 1959). Second, proteolysis can serve as an important method for modification of the covalent structure of biologically active proteins (Anfinsen and Redfield, 1956). 

A number of studies have been designed to determine the nature of the mechanism of proteolysis with a specific enzyme and substrate. Ginsberg and Schachman (1960a,b) concluded that chymotryptic hydrolysis of insulin probably proceeds by the all or none mechanism, whereas peptic hydrolysis of ribonuclease follows a zipper mechanism. 

In other studies it appears that the kinetics of digestion of human serum albumin by pepsin and chymotrypsin follow the all or none mechanism, whereas tryptic action is of the zipper type (Kaminski and Tanner, 

Human 7-globulin Horse diphtheria antitoxin Human serum albumin Insulin 

Northrop (1941-1942), Rothen (1941-1942) Lapresle e al. (1959), Kaminski and Tanner (1959) Nicol (1960), Carpenter and Baum (1962) 

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Table XVI gives a partial list of native proteins that have been hydrolyzed with proteolytic enzymes. A discussion of the interpretation of each example listed is beyond the scope of this review, but a few comments concerning certain features of proteolysis are ivarranted. The mechanism of enzymatic hydrolysis of native proteins was studied in detail by Tiselius and Eriksson-Quensel (1939), who examined the action of pepsin on ovalbumin. Two mechanisms of proteolysis were considered by these workers. In the first mechanism the enzyme hydrolyzes all susceptible peptide bonds in one substrate molecule before hydrolysis of a second molecule begins. This type of mechanism has been described by Lmderstrpm-Lang (1952) as the all or none type. In the second mechanism, the enzyme hydrolyzes the single, most susceptible bond in all substrate molecules before hydrolysis of other bonds occurs. This mechanism is called the zipper type. Hydrolysis of a protein can proceed by either of the two mechanisms or by a mechanism which has features of both types. General aspects of the problem have been reviewed and theoretical equations which describe the kinetics of ea( h mechanism have been derived (Linderstr0m-Lang, 1952, 1953).

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