Hydrophobicity of biosurfaces as shown by chemoreceptive Thresholds inTetrahymena, Physarum andNitella

Abstract

Responses (chemotaxis and changes in membrane potential) ofTetrahymena, Physarum, andNitella against aqueous solution of homologous series ofn-alcohols,n-aldehydes andn-fatty acids were studied for clarifying the hydrophobic character of chemoreceptive membranes. Results were: (1) All organisms studied responded to homologous compounds examined when the concentration of these chemicals exceeded their respective threshold,C _th , and the response,R, were expressed approximately asR=α log (C/C _th ) forC>C _th , (2) Increase of the length of hydrocarbon chain in homologues decreasedC _th . Plots of logC _th against the number of carbon atoms,n, inn-alcohols,n-aldehydes andn-fatty acids showed linear relationships as represented by logC _th =−An+B. A andB are positive constants for respective functional end groups of the chemicals and biological membranes used. The above empirical equation was interpreted in terms of the partition equilibrium of methylene groups between bulk solution and membrane phase. ParameterA was shown to be a measure of hydrophobicity of the membrane, andB represented the sensitivity of chemoreception of the membrane. (3) Thresholds,C _th , for various hydrophobic reagents were compared with those of human olfactory reception,T. Plots of logT against logC _th fell on straight lines for respective organisms with different slopes which were proportional to parameterA.