Evidence for two molecular forms of solubilized vasopressin receptors in rat kidney membranes. Regulation by guanyl nucleotides.

As previously reported, it is possible to solubilize vasopressin-receptor complexes formed in rat kidney membranes by the use of Triton X-100. Ultracentrifugation on sucrose gradients and elution through molecular sieving columns of these soluble extracts revealed the existence of two molecular forms of vasopressin-receptor complexes (molecular weight = 200,000 and 100,000, respectively). These two molecular forms of vasopressin-receptor complexes can be partially purified and exhibit different properties: (a) The light form is more sensitive to thermal dissociation than is the heavy form. (b) The presence of guanyl nucleotide affects the dissociation rate of only the heavy form of the vasopressin-receptor complex. (c) The light form seems to be convertible to the heavy form by increasing the duration of incubation between the membranes and the tritiated hormone. (d) Guanyl nucleotides affect the distribution of the two molecular forms of the receptor (decrease of the relative amount of the heavy form). These data provide evidence for interaction between vasopressin-receptor complexes (light form) and another protein component, which may be a GTP-binding protein.