The light-activated phosphorylation of rhodopsin under in-vivo- and in-vitroconditions is known since a long time. On contrary little is known about dephosphorylation.The quantitative dephosphorylation of highly phosphorylated bovine rhodopsin is not yet described. I describe optimized conditions to dephosphorylate highly phosphorylated rhodopsin from bovine (PG 5 -6 mol/mol rhodopsin) quantitatively with different extracts from ROS or from the whole retina. Experiments, using "whole ROS" as a source for phosphatase(s) are shown. Further first results of experiments to purify phosphatase(s) from retina-extracts areshown. 1) I found phosphatase-activity in different extracts from ROS and from retina and in "whole ROS". Phosphatase (s) from ROS is (are) isotonically extracted, but hypotonic extracts contain slightly higher phosphatase-activity. About only 20 % of the activity remains in the pellets after extraction. Therefore phosphatase(s) seem(s) to be soluble protein(s) of the Rod Outer Segments. Activity of hypotonic retina-extract is about 60 times higher than the activity of ROS-extract. I discuss the possibility of the existence of different phosphatases in these different extracts. A quantitative dephosphorylation of rhodopsin with extracts from ROS or from retinaoccurs only in the presence of a nonionic detergent (Octylglucosid). In the absence of detergent phosphorylated rhodopsin is dephosphorylated to about 30 - 40 % only. I discuss increased activity in presence of detergent as a possible influence on the substrat or on the phosphatase(s) itself The results indicate an influence of the detergent on the phosphatase(s) but not on the substrat. The pH-optimum for the phosphatase-activity is at pH 5.7; therefore the phosphatase(s) is (are) adjoined to "acid phosphatases". Depending on temperature a considerable loss of phosphatase-activity in the extracts was found during the experiments. The loss of activity is highly depressed in presence of DTT. Several factors inhibit phosphatase-activity. An ionic strengh of about 250 mM NaCl inhibits the activity half-maximal. Sodiumphosphat inhibits halfmaximal at a concentration of 10 mM and ATP inhibits about 90 % at a concentration of 5 mM. Using "whole ROS" as a "phosphatase-source" I found in contrast to extracts no quantitative dephosphorylation of rhodopsin in the presence of detergent. "Whole [...
