Study of macroamylase complexes

The structure of abnormally large-sized serum amylases (macroamylases) of 4 patients was investigated. Incubation of purified human salivary amylase labelled with ¹²⁵Iodine with each macroamylase sera resulted in an increase in the apparent molecular size of some of the ¹²⁵I-amylase while incubation with normal sera had no such effect. Thus, macroamylase appears to consist of normal amylase bound in the form of a complex by some abnormal substance in the serum. The binding characteristics of these substances were quite variable. Two macroamylase complexes showed marked dissociation during gel filtration while the other two were relatively stable. The addition of excess human, baboon, hog, and fungal amylase to the sera suggested that the amylase-binding substances of different subjects had variable affinities for the different forms of amytase. The binding substance of one subject, which had previously been shown to be IgA, had a marked affinity for hog amylase. This subject had received hog pancreatic supplements for many years and it is possible that her binding substance represents an IgA immune response to hog pancreatic amylase with crossreactivity for human amylase. The nature of the binding of the other 3 macroamylases is uncertain although the inability to bind fungal amylase suggests that these complexes were not enzyme-substrate interactions.