Metastabilities of proteins around a pseudoinvariant point. Activities of CO2(aq), NH3(aq), H2S(aq) and H2O were calculated using a buffer consisting of the proteins from the METXX organisms listed in Table 1. The variables set in the buffer calculation were activities of proteins equal to 10-3, T = 100°C, P = 1000 bar, log = -58 and pH 7. The diagrams show the variation of protein metastability as a function of (a) temperature and pressure and (b) log and pH. The dashed line in (b) represents the lower stability limit of H2O at this temperature and pressure.