MOLECULAR-WEIGHT ALTERATIONS OF ALPHA-1 PROTEINASE-INHIBITOR IN EQUINE BRONCHOALVEOLAR LAVAGE FLUID

The equine alpha-1 proteinase inhibitor (alpha 1PI) system differs fro m that of man in that the equine system consists of four closely-linke d genes (Spi1-Spi4) whereas in man, a single gene encodes for alpha 1P I. We have previously found differences in the proportion of the Spi p roteins in equine serum and bronchoalveolar lavage fluid (BALF). We th erefore wished to determine whether, as reported in man, there was any molecular weight difference between the Spi proteins in serum and BAL F. alpha 1PI and albumin from equine BALF migrated further towards the anode compared with serum alpha 1PI on native polyacrylamide gel elec trophoresis (PAGE) although the difference was only significant for al pha 1PI. Sodium dodecyl sulphate-PAGE (SDS-PAGE) showed that a mean de crease in molecular weight of 1.5 kDa for alpha 1PI and 1.3 kDa for al bumin had occurred in BALF. These findings were observed in control an imals and in those with symptomatic or asymptomatic chronic obstructiv e pulmonary disease. The mechanism of this decrease in molecular weigh t of alpha 1PI is likely to differ from reports of alpha 1PI cleavage by bacterial proteinases in man since the molecular weight change was relatively small and loss of trypsin inhibitory activity did not occur . Nor, in our system, was there evidence of bacterial infection. Damag e by endogenous proteinases or glycosidases at a site other than the r eactive site may be involved but the resultant effect on the efficienc y of the antiproteinase screen of the lower respiratory tract is uncer tain.