Table 1.
Experimental reversal potential values and calculated permeability ratios of ampicillin, its degradation product (penicilloic acid) and benzylpenicillin through the OmpF pore under tri-ionic conditions
The permeability ratio of PK+/PCl− = 4:1 (pH 8), PK+/PCl− = 2.8:1 (pH 6), and PK+/PCl− ≅ 2:1 (pH 4) for OmpF has been determined independently under bionic conditions (see also Ref. 52) and was fixed during fitting of Vrev (tri-ionic) (for details see supporting data). The symbols indicate: *, pH 8; **, pH 6; ***, pH 4, and # at p4, the probability of ampicillin to carry a positive charge is n @ 0.13 (Table S2), however, it is very difficult to correlate the measurement of Vrev at this pH on a defined concentration of ampicillin during the course of the measurements due to the accelerated chemical decomposition of ampicillin.
| Substrate | Substrate (cis) | KCl (cis/trans) | Vrev (n = 3) | PK+/PCl−/Pampicillin |
|---|---|---|---|---|
| mm | mV | |||
| Ampicillin-K* | 80 | 30 mm | 21.5 ± 4.8 | 4:1:0.75 |
| Ampicillin-K* | 50 | 30 mm | 15.8 ± 3 | 4:1:0.75 |
| Ampicillin-K*** | 80# | 30# mm | 28 ± 7 | 4:1:1.3 |
| Penicilloic-acid-K** | 72* | 30 | Vrev = 31 ± 6 | 4:1:10−4 |
| Benzylpenicillin-K** | 80 | 30 mm | 23.5 ± 3 | 2.8:1:0.3 |