Specific binding sites for potassium, which may be components of the carriers for active transport for K in Chlorella, were characterized by their capacity to bind rubidium. A dense suspension was allowed to take up Rb86 from a low concentration of Rb86 and a high concentration of ions which saturate non-specific sites. The amount bound was derived from the increase in the external concentration of Rb86 following addition of excess potassium. The sites were heterogeneous. The average affinity of Rb and various other ions for the sites was determined by plotting the degree of displacement of Rb86 against log molar concentration of the individual ions. Interpolation gave the concentration for 50 per cent displacement of Rb, which is inversely related to affinity. The order of affinity was not changed when the cells were frozen, or boiled either in water or in 70 per cent ethanol. The affinity is maximal for ions with a crystalline radius of 1.3 to 1.5 A and a high polarizability, and is not related to the hydrated radius or valency. It is suggested that binding groups in a site are rigidly arranged, the irregular space between them being 2.6 to 3.0 A across, so that affinity is high for ions of this diameter and high polarizability.
Article| May 01 1962
Specific Binding of Rubidium in Chlorella
From the Department of Agriculture, University of Oxford, England.
Dr. Cohen's present address is the Department of Botany, The Hebrew University of Jerusalem, Israel
Received: December 18 1961
Online Issn: 1540-7748
Print Issn: 0022-1295
Copyright, 1962, by The Rockefeller Institute Press
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Dan Cohen; Specific Binding of Rubidium in Chlorella . J Gen Physiol 1 May 1962; 45 (5): 959–977. doi: https://doi.org/10.1085/jgp.45.5.959
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