Are Serum Lipoproteins Esterases?

The immune precipitates of high-density lipoprotein of duck serum with rabbit antisera are active on an esterase substrate, while the high-density lipoprotein itself is not active. The immune precipitates formed by high-density lipoprotein with isolated immunoglobulins, either in agar gel or in liquid medium, were also shown to be inactive, Such inactive immune precipitates can become active through interaction with a component of rabbit serum. Investigations on the conditions of the reaction and first observations concerning the nature of the activating component are reported. [ABSTRACT FROM AUTHOR]