Enzymes digestive proteases

Different enzymes are used for digestion. Proteases are the most widely used group of enzymes. The most commonly used proteases are... 

Rapid degradation of proteins is often induced at certain stages of differentiation. For example, sporeforming bacteria contain a protease that becomes activated upon germination of the spore.131 Within minutes this enzyme digests stored proteins to provide amino acids for the synthesis of new proteins during growth. 

In the manufacture of baby foods, enzymes called proteases are used to pre-digest the protein part of the baby food. This is because young babies are unable to digest protein molecules. 

Pis inhibit the digestive protease enzyme of HIV, which it uses to break the proteins of healthy cells into smaller pieces. These infected smaller pieces of protein then carry on infecting new host cells. Pis therefore slow down HIV proteases and subsequently inhibit the infection of new cells [94]. 

Fig. 8. The network structure of type IV collagen as deduced from electron microscopy of fragments solubilized with proteases (Timpl et at., 1981). The top left micrograph shows the short form of the 7 S region. In the top right, a more limited enzyme digestion allows a portion of the helical domain of each molecule to remain linked to the 7 S domain. The bottom left micrograph shows isolated dimeric NCI fragments and, at the lower right, dimeric triple helical material connected in the center by the NCI domain.

Dietary protein is the principal source of fixed nitrogen in higher animals. In digestion, proteins are hydrolyzed by a series of hydrolytic enzymes in the stomach and the small intestine to peptides and amino acids, which are absorbed from the lumen of the gastrointestinal tract. These enzymes are known collectively as proteolytic enzymes, or proteases, and belong to the class of enzymes called hydrolases (Chap. 8). 

There are also a number of enzymes that degrade organic N compounds, inside or outside the cell, thereby making N available for assimilation or uptake, respectively. Examples we will consider include urease, amino acid oxidases, and extracellular peptidases (MulhoUand et al., 2002 MulhoUand and Lee, in revision. Chapter 7 by MulhoUand and Lomas, Fig. 2, this volume Table 32.1). In addition, for heterotro-phic organisms, digestive enzymes, especially proteases, are important for internal N cycling, recouping cellular N, and excretion. 

Overview Heterotrophs represent a major sink for primary production, and thus a critical part of the marine N cycle. In the pelagic realm, there have been attempts to estimate zooplankton grazing (both micro- and macro-zooplankton) using two major enzymatic approaches activities of digestive enzymes (especiaUy proteases in the case of N) (e.g., Gonzalez et al, 1993) and the activity of GDH, the... 

The enzymes called proteases are necessary for the digestion of proteins. A newly proposed treatment for acquired immune deficiency syndrome (AIDS) involves the use of protease inhibitors, and as AIDS is an immunodeficiency disease, with cancer sometimes described in the same way, there may be a connection. (AIDS is by most accounts caused by the retrovirus HIV, and cancer may in some instances be traced to retroviruses.)... 

In enzymic digestions, the structures of the released peptides will, of course, depend upon the specificity of the particular protease. Often the peptides exhibit a very undesirable bitter flavor. For example, Fujimaki et al. (22) have characterized seven bitter peptides in peptic hydrolysates of soybean proteins. Almost all the bitter peptides had leucine at the N or C termini, and the bitterness of the peptides could be reduced by treatment with exopeptidases such as carboxypeptidase A. 

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