Aprotinin-like isoinhibitors in bovine organs

Previous studies have shown that bovine spleen contains, besides aprotinin (bovine pancreatic trypsin inhibitor, BPTI), three iso-inhibitors (I-III), which are structurally and functionally very similar to BPTI. The primary structure of inhibitors I and II indicates that they are not post-translational products of BPTI, in agreement with independent findings on two homologous genes reported to be present in the bovine genome, which encode BPTI and inhibitors I and II, respectively. A careful reinvestigation on the occurrence of these inhibitors in various bovine organs is presented in this paper, based on their isolation with standard biochemical techniques and on functional and structural studies. All data indicate that the same isoinhibitors found in spleen are also present, besides BPTI, in organs such as lung, liver and pituitary gland, where they were never found before. BPTI and inhibitor II always prevail.