a The mitochondrial membrane potential can be measured by assessing the distribution of a membrane-permeant cation between the matrix and the external medium (Bioenergetics 4 pgs 66-69; see also pgs. 47-49). One such cation is tetraphenyl phosphonium (TPP+). A sample chamber containing a TPP+-specific electrode was filled with aerated pH=7.4 buffer containing succinate (as electron donor), oligomycin (to inhibit ATP synthase), and 10-5 mol 1-1 TPP+, and then maintained at a temperature of 37C. Mitochondria were injected into the chamber to a concentration of 1 mg protein ml-1 following which the TPP+ concentration measured with the electrode fell to 6.5 x10-6 mol 1-1. The volume of the mitochondrial matrix was determined by the sucrose-impermeable space method (Bioenergetics 4 page 67) to be 1ml (mg mitochondrial protein)-1. Determination of the electrical gradient (A4) across the inner membrane of actively respiring mitochondria S [TPP* | matris log10 (TPP+]external AV (external-matrix) 2.3 RT { nF Where (in addition to those defined in question 1): o n= charge on the ion o F = 96.5 kJ mol-1 V-1 (Faraday constant) You may give the answer in either V or mV