Proteases attract a growing interest as their vital role becomes apparent in ever more biological processes. This important group of enzymes includes serine proteases. This enzyme is responsible for the elastin degradation that occurs in emphysema, a serious lung disease. This chapter discusses cellular and tissue serine proteases. Most of the serine proteases, such as the pancreatic enzymes chymotrypsin, trypsin, and elastase, are believed to have evolved from a common ancestor. They are assumed to have acquired different specificities by mutation of the genes descended from an evolutionary precursor. This process is a typical example of divergent evolution. The evolutionary relationship of homologous serine proteases can be estimated from the number of insertions and deletions (gaps) arising from optimally aligned sequences of the enzymes. The amino acid sequences of the pancreatic enzymes are homologous; the structurally and catalytically important residues are conserved.
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