On the molecular structure of some prostaglandin receptors.
Hypotheses are presented of the detailed molecular structure of two prostaglandin receptors both concerned in tumor-promotion processes. These structures have been derived by the comparison  of the molecular structure of agents active at the site with (i) a simple theoretical protein structure and (ii) the known x-ray structure of phospholipase A2. The first model receptor is stimulatory to the tumor-promotion process and may be located on the control system for ornithine decarboxylase. The binding of PG here is cooperative with the binding of Ca++. Naturally-occurring agonists at this receptor may include members of the cathartic class of drugs such as colocynth, chrysarobin, etc. Naturally-occurring antagonists at this site may include a number of anti-tumor compounds such as datiscoside. The second model receptor (PGE1) is inhibitory to the tumor-promotion process and is located at a specific allosteric site on the x-ray-determined structure of phospholipase A2. This site overlaps for one for lysolecithin (excitatory), for which tumor-promoting phorbol esters such as TPA are agonists and some anti-tumor drugs such as maytansine may be antagonists.
D000970:Antineoplastic Agents / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002273:Carcinogens / Q000494:pharmacology; D055598:Chemical Phenomena; D002621:Chemistry; D008954:Models, Biological; D010741:Phospholipases A; D054467:Phospholipases A2; D011448:Prostaglandin Antagonists; D011458:Prostaglandins E; D011956:Receptors, Cell Surface; D011982:Receptors, Prostaglandin
D000970:Antineoplastic Agents; D002273:Carcinogens; D011448:Prostaglandin Antagonists; D011458:Prostaglandins E; D011956:Receptors, Cell Surface; D011982:Receptors, Prostaglandin; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium