Entrapment of nonproteolytic enzymes in alpha 2-macroglobulin using immobilized trypsin

Entrapment in human alpha 2-macroglobulin (alpha 2M) of non-proteolytic enzymes was achieved with the help of trypsin covalently attached to Sepharose matrix. While it was also possible to achieve entrapment by the exposure of the alpha 2M: enzyme mixtures to soluble trypsin, use of the immobilized proteinase resulted in improved entrapment yields and also prevented the coentrapment of trypsin. Both soluble and immobilized trypsin transformed alpha 2M to the electrophoretically fast form but the immobilized trypsin required relatively longer incubation to bring about the transformation. Horseradish peroxidase was entrapped in higher yield in alpha 2M compared to the relatively high-molecular-weight invertase. alpha 2M-entrapped peroxidase and invertase appeared highly accessible to their respective substrates, as evident from their relatively unaltered Km values. alpha 2M-associated invertase, in spite of its large dimensions, failed to crossreact with the rabbit anti-invertase antiserum, indicating its physical entrapment rather than any other form of association.