title: The concept of chemical capacitance, A critique.
abstract: The concept of chemical capacitance as introduced by Hong and Mauzerall (Proc. Natl. Acad. Sci. U.S.A. 1974. 71:1564) is critically reexamined. This novel capacitance was introduced to explain the time-course of flash-induced photocurrents observed in lipid bilayer membranes containing porphyrins. According to Hong and Mauzerall, the chemical capacitance results from a combination of three fundamental capacitances: the geometric membrane capacitance and the two interfacial double layer capacitances. The concept of chemical capacitance is questioned for the following reasons: (i) The system analysis is insufficiently determinate. (ii) The measured chemical capacitance is approximately 0.16% of that predicted by the theory. (iii) The fact that only 20% of the membrane area is illuminated was not considered in the analysis. The latter point offers an alternative explanation of the capacitance in question: this capacitance may reflect that fraction of the total membrane capacitance that is photochemically active. If so, the concept of chemical capacitance lacks general significance.
mesh_terms: D001436:Bacteriorhodopsins / Q000378:metabolism; D055592:Biophysical Phenomena; D001703:Biophysics; D004563:Electrochemistry; D008027:Light; D008051:Lipid Bilayers; D008566:Membranes / Q000378:metabolism*; D008954:Models, Biological; D010777:Photochemistry; D010788:Photosynthesis; D012243:Rhodopsin / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D001436:Bacteriorhodopsins; D012243:Rhodopsin