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. Author manuscript; available in PMC: 2011 Jun 23.
Published in final edited form as: Curr Opin Biotechnol. 2010 Jun 18;21(4):439–476. doi: 10.1016/j.copbio.2010.05.002

Figure 13.

Figure 13

Basic concept of monitoring the activity of a membrane-active enzyme, phospholipase D (PLD), on planar lipid bilayers. Enzyme activity is recorded by changes in single channel conductance of gramicidin pores. (a) As PLD hydrolyzes electrically neutral phosphatidylcholine (PC) lipids and produces negatively charged phosphatidic acid (PA) lipids, the electrostatic accumulation of cations close to the membrane surface leads to a significant increase in channel conductance of gramicidin pores. Negative charges are shown in red, and positive ions are shown in blue. (b) Corresponding current versus time recordings before and after addition of PLD. Figure adapted from reference [23•] with permission.