PURIFICATION AND CHARACTERIZATION OF THE HEAD-ACTIVATOR RECEPTOR FROM A MULTIHEADED MUTANT OF CHLOROHYDRA-VIRIDISSIMA

In hydra the neuropeptide head activator (HA) is responsible for head-specific growth and differentiation processes. The effects of HA are mediated by high and low affinity receptors on hydra cells. In the current study HA receptors from a multi-headed mutant of Chlorohydra viridissima were solubilized from the membrane fraction using 1% Triton X-100 and 2.5 M urea. Scatchard analysis showed that the solubilized receptor had a K(d) of 1.55 x 10(-9) M, indicating the low affinity subtype of the HA receptor. The solubilized receptor was purified by DMAE chromatography and subsequent affinity chromatography to homogeneity. SDS-PAGE revealed a single protein band with a molecular mass of % +/- 4 kDa. The native receptor eluted during gel filtration as a 113 kDa protein, and focussed with an isoelectric point of 4.8.