T H E Characterization and Localization of Frog Skin

Frog skin cholinesterase is largely of the serum (pseudocholinesterase) type. For whole skin, the activity at 10 --1 ~ AcChC1 is 4.9/~l./mg. N/hr. Tela subcutanea isolated by dissection exhibits an activity of 65 #l./mg. N/hr. at 10 --j ~ AcChC1. Since about one-tenth of the nitrogen of the skin is located in the tela subcutanea, it is estimated that more than 90 per cent of the enzyme is associated with this tissue layer. Kirschner (8) has reported that inhibitors of cholinesterase inhibit active sodium transport in frog skin. These inhibitors are more effective when applied to the inside of the skin than when applied to the outside. The action of each inhibitor on sodium flux has the same reversibility properties as its action on the enzyme. Thus, eserine, a reversible inhibitor of cholinesterase, reversibly inhibits active sodium transport, while tetraethylpyrophosphate, an irreversible inhibitor of the enzyme, exhibits irreversible inhibition of transport. Van der Kloot (10) has presented evidence that the sodium pump in frog muscle requires cholinesterase activity. He measured the equilibrium intracellular sodium concentration and the residual cholinesterase activity of frog sartorii which had been bathed in graded concentrations of physostigmine eserine, a cholinesterase inhibitor capable of penetrating into the muscle fibre. I t was found that the equilibrium intracellular sodium concentration paralleled the degree of cholinesterase inhibition, the 50 per cent values both falling at about 10 -~ ~ physostigmine. Despite the occurrence of high cholinesterase activities in tissues in which active sodium transport is observed to occur, and the striking effects of cho* Supported by grants from the National Science Foundation and the United States Public Health Service, administered by B. T. Scheer. These results form a part of a thesis submitted to the Graduate School, University of Oregon, in partial fulfillment of the requirements for the Ph.D. degree. :~ Address after September 1, 1958: Department of Zoology, University of Missouri, Columbia, Missouri. 1129 J'. GEN. P~YSIOL., 1958, Vol. 41, No. 6 The Journal of General Physiology on Jne 1, 2017 D ow nladed fom Published July 20, 1958