[Certain features of monoclonal rheumatoid immunoglobulin M fragmentation by "hot" trypsin]

Using analytical ultracentrifugation and affinity chromatography, it has been shown that "hot" trypsin (hydrolysis at 58-60 degrees C) releases two types of fragments from the monoclonal (Waldenstrom disease) immunoglobulin M possessing a rheumatoid activity (IgM-RF). The first fragment corresponds to a normal Fab-fragment as can be judged from its molecular weight. The other fragment designated as a (Fc)*5-fragment has a much higher molecular weight as compared with typical (Fc)*5-fragment released from non-rheumatoid IgM. According to calculations, the (Fc)*5-fragment retains two uncleaved Fab-regions and displays a rheumatoid activity. The Fab-fragments pool cleaved from IgM-RF consists of non-rheumatoid and rheumatoid components at an approximate ratio of 3:1. It seems, therefore, likely, that ten Fab-regions of IgM-RF are nonidentical with regard to their functional and structural properties. Most of those do not possess a rheumatoid activity and are more readily cleaved from IgM-RF by "hot" trypsin in comparison with rheumatoid active fragments.