INTERACTION OF SYNTHETIC PEPTIDE OCTARPHIN WITH RAT ADRENAL CORTEX MEMBRANES
Synthetic peptide octarphin (TPLVTLFK, the fragment 12-19 of  endorphin), a selective agonist of non opioid endorphin receptor, was labeled with tritium to specific activity of 28 Ci/mmol. The binding of [3H]octarphin to rat adrenal cortex membranes in norm as well as after cold and heat chock was studied. It was found that [3H]octarphin binds to membranes with high affinity and specificity: Kd1 = 36.3  2.5 nM, Bmax1 = 41.0  3.8 pmol/mg protein. The specific binding of [3H]octarphin to the membranes was inhibited by unlabeled  endorphin (Ki = 33.9  3.6 nM) and agonist of non opioid receptor decapeptide immunorphin (Ki = 36.8  3.3 nM); unlabeled naloxone and [Leu5] and [Met5]enkephalins, as well as , and  endorphins and corticotrophin tested in parallel were inactive (Ki > 1 M). Both cold and heat shock led to a decrease in the binding affinity: Kd2 = 55.6  4.2 nM and Kd3 = 122.7  5.6 nM, respectively. The binding capacity did not change. Thus, even a short term thermal shock causes a significant change in the non opioid  endorphin receptor binding capacity of adrenal cortex membranes.