Sulfhydryl proteases, protease

Sulfhydryl proteases, see Actinidin, Papain Superoxide dismutase, Cu,Zn (Richardson et al., 1975)... 

Thermolysin belongs to a class of proteases (called neutral proteases) which are distinct from the serine proteases, sulfhydryl proteases, metal-loexopeptidases, and acid proteases. Neutral proteases A and B from Bacillus subtilis resemble thermolysin in molecular weight, substrate specificity, amino acid content, and metal ion dependence. Since physiological substrates are most likely proteins, it is difficult to design simple experiments that can be interpreted in terms of substrate specificity and relative velocities. Therefore, studies of substrate specificity and other kinetic parameters must be carried out on di- and tripeptides so that details of the mechanism of catalysis can be obtained and interpreted simply. 

Proteolytic enzymes can be divided into the following four groups the acid proteases, the serine proteases, the sulfhydryl proteases, and the metal-containing proteases. 

Liener, I.E. 1974. The sulfhydryl proteases. In Food related enzymes, ed. J.R. Whitaker. Advances in Chemistry Series 136. Washington, DC American Chemical Society. 

B Elimination has been used to show differences among the disulfide bonds in various proteins including the ovomucoids (54). The e-elimination reaction has also been used to replace the hydroxyl group of the essential serine residue of subtilisin with a sulfhydryl group (55). The thiolsubtilisin had a small fraction of the activity of subtilisin but it has been quite useful in mechanistic studies of the serine and sulfhydryl proteases. 

Among the proteolytic enzymes, the plant proteases are the most widely used in the food industry. Most of the plant proteases which have been studied are characterized by a free sulfhydryl group which is essential for their activity. The most important of these so-called sulfhydryl or thiol proteases are papain, ficin, and bromelain. Since the literature on these enzymes has been the subject of several recent reviews (i, 2, 3, 4), major emphasis is placed in this presentation on the use of these enzymes in the food industry. Some of the more recent developments relating to the structure and function of the sulfhydryl proteases are discussed. 

One of the most characteristic differences between papain and the other sulfhydryl proteases, ficin and bromelain, is the absence of carbohydrate in papain. Glycopeptides have been isolated from ficin (48) and bromelain (49, 50, 51, 52). In the case of bromelain the carbohydrate moiety composed of mannose, xylose, fucose, and N-acetylglucosamine is covalently linked to an asparagine residue of the peptide chain through a glucosamine component of the sugar moiety (51,52). 

R. M. Silverstein and F. J. K6zdy. Separation and characterization of sulfhydryl proteases from stem bromelain. Fed. Proc. Fed. Am. Soc. Exp. Biol. 29 929Abs (1970). 

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