Studies on elastase and elastin. I. Assay and properties of elastase.

As early as 1890, Ewald (1) showed that extracts of pancreas were able to dissolve the elastic fibers of connective tissue. In 1950, Balo and Banga (2) described the properties of a purified enzyme obtained from defatted pancreatic powder, distinct from trypsin and chymotrypsin, and capable of dissolving elastic fibers either in tissues or in test tubes. Lewis, Williams, and Brink (3) have since obtained this enzyme in a very active form and assigned to it a molecular weight of 25,000. It is a proteolytic enzyme which releases approximately I30 moles of Nterminal residues per 100,000 g of substrate, when it acts on elastin (4). So far elastase has not been obtained in a pure form. Products of a high degree of activity have been shown to be paucidisperse by chromatographic analysis (5) or electrophoresis (6). A considerable amount of proteolytic activity toward various proteins, such as casein and hemoglobin, accompanies the elastolytic enzyme (7), and opinions are divided as to whether the enzyme activity belongs to one or several proteins (8, 9). Some of the divergent opinions expressed in the literature seem to be due to the variety of assays employed to titrate elastase. This paper will describe three assays. One is based upon the amount of elastin which is solubilized by the enzyme; the two others measure the appearance of free amino groups attending the breakage of peptide bonds in the substrate. Some of the properties of the enzyme will be studied with the aid of these assays. By the use of a chromatographic procedure, it will be demonstrated that elastase can be divided into two active elastolytic fractions, one of which contains most of the nonspecific proteolytic activity and another which is poor in that activity.