Concerning the Mechanism of Complement Action

Abstract

Summary C′1 and TAMe esterase activity can be eluted from sensitized sheep red cells containing C′1 activity by ethylenediaminetetraacetic acid. On dialyzing the supernatant from cells so treated against a low ionic strength buffer, both activities can be recovered. The C′1 activity eluted from red cells in this fashion can be detected with case by a two-step procedure of adding the “eluate” to sensitized cells, washing and then adding an R1. If an R1, sensitized cells and the “eluate” are added together little or no evidence for C′1 activity is obtained. The properties of the enzyme when removed from the cell are the same so far as studied as when the enzyme is attached to the cell. When sensitized cells are treated with the eluate not only does C′1 activity attach itself to the cells but esterase activity as well. Allowing the eluate to stand in the cold at pH 3.3, affects its TAMe esterase activity little of at all; however, the C′1 activity and the ability of the esterase to attach to sensitized cells is destroyed and, as kinetic studies showed, destroyed to the same extent. In explanation of these latter observations the hypothesis was evoked that the C′1 molecule contains two distinct sites, a binding site and an enzymatic site, and both are required in order for the molecule to manifest C′1 activity.