Aggregation properties of the 1,25-dihydroxyvitamin D3 receptor from chick intestinal cytosol.

The sedimentation behavior of the chick intestinal cytoplasmic receptor for 1..cap alpha..,25-dihydroxyvitamin D/sub 3/ has been examined in buffers containing varying concentrations of KCl. The receptor, which sediments at 3.7 S in 0.3 M KCl, was shown to aggregate to species sedimenting at approximately 5 S in 0.06 M KCl and 6.2 S in the absence of KCl. Depending on the preparation and route used to label the receptor with 1,25-dihydroxy(/sup 3/H)vitamin D/sub 3/, larger aggregates which sedimented to the bottom of sucrose gradients were also seen. Aggregated receptor like the 3.7 S species specifically binds 1,25-dihydroxyvitamin D/sub 3/ with high affinity and low capacity. In the absence of KCl, aggregated receptor eluted as a heterogeneous peak near the void volume of a Sephadex G-200 column. In 0.3 M KCl, receptor eluted from the same column with an apparent molecular weight of 60,000. Aggregated receptor prepared from G-200 columns in the absence of KCl could be converted back to a 3.7 S species by adding KCl to a concentration of 0.3 M. Receptor aggregation was shown to be caused, at least in part, by the interaction of receptor with other cytoplasmic components which contaminate crude receptor preparations. These factors aremore » present in both liver and intestinal cytosol. Aggregation of receptor, which was maximal in cytosol labeled with 1,25-dihydroxy(/sup 3/H)vitamin D/sub 3/ at 0/sup 0/C, was gradually lost withconcomitant increases in 3.7 S material when preparations were incubated at 25/sup 0/C. This loss of receptor aggregation appears to be due, at least in part, to changes in the receptor molecule itself rather than the inactivation or degradation of cytoplasmic aggregating factors.« less