Macroamylase immunoglobulins show high affinity for animal and human amylases

We have examined the affinity shown by the immunoglobulin fraction from each of five sera containing macroamylase for amylases from different sources: human saliva or human, porcine, or ovine pancreas. High affinity constants, 0.4 X 10(10) to 7.2 X 10(10) L/mol, were found in competitive binding experiments with human or porcine pancreatic amylase. All but one serum yielded linear Scatchard plots, indicating that in most sera the amylase-binding immunoglobulins are homogeneous, possibly monoclonal. The immunoglobulin fractions from different sera differed in their specificity: two of them bound all four types of amylases, whereas two bound only one type. Three of the five immunoglobulin fractions showed considerably higher affinity towards one or both of the animal amylases than towards the human ones, and may be primarily directed against some animal amylase.