ANALYSIS OF 1-ALPHA,25-DIHYDROXYVITAMIN-D(3) RECEPTOR IN CELL-EXTRACTS WITH LOW-PROTEIN CONCENTRATION

An unacceptable loss of tritiated 1,25-dihydroxyvitamin D3 [1,25-(OH)2 D3] to the wall of the reaction tubes constituted an obstacle when exa mining C3H/10T1/2 Cl 8 cells for 1,25-(OH)2D3 receptor. The loss of tr acer in low protein cell extracts could be strongly reduced by incubat ing the cell extracts in polyethylene tubes and in the presence of ine rt peptides prepared by digestion of gluten proteins. When incubated i n buffer the recovery of tracer increased from 3 to 45% by using polye thylene tubes instead of sodium-glass tubes. However, the presence of a sufficient amount of inert peptides in the buffer significantly incr eased the recovery of tracer to 89%. This procedure improved the satur ation binding analysis of the 1,25-(OH)2D3 receptor in the C3H/10T1/2 Cl 8 cells using the hydroxylapatite assay.