Elastases and elastin degradation.

The metabolic turnover of mature elastin fibers in adult animals is relatively slow. Although only small amounts of elastin are degraded normally, increased degradation and fragmentation of elastic fibers may play a significant role in disease processes. Elastinolytic enzymes are found in microorganisms, snake venoms, and in a number of mammalian cells and tissues, including pancreas, polymorphonuclear leukocytes, and macrophages. Elastinolytic enzymes fall into all 4 classes of proteinases (aspartic, cysteine, serine, and metallo) and show a spectrum of different specificities. All elastases studied to date have catalytic activity against protein and peptide substrates other than elastin. The presence of elastase activity is a virulence factor associated with the pathogenicity of Pseudomonas and other bacteria, dermatophytic fungi, and necrosis by rattlesnake venoms. Only elastinolytic enzymes are capable of inducing experimental pulmonary emphysema. Elastin degradation mediated by living macrophages and trophoblasts is confined to the immediate pericellular environment. Destruction of mature elastin by other mammalian elastases is probably the result of an imbalance in the normal inhibitor-proteinase ratio. The major plasma inhibitors contributing to the regulatory balance are alpha 1-proteinase inhibitor and alpha 2-macroglobulin.