values between 5.0 and 7.0 could be explained because globular
proteins generally are most stable to denaturation at pH values
close to their pI (Privalov & Khechina, 1974). Ber e 1 isoforms have
pI values ranging from pH 5.5 to 8.1. In the protein preparation
investigated, the most abundant isoforms had pI values around
pH 8 (van Boxtel et al., 2006). At pH 7.0 the enthalpy of unfolding
was observed to be highest (Table 1), most likely because this pH
value is closest to the most abundant pI value in this protein preparation
(van Boxtel et al., 2006).
The denaturation of Ber e 1 at low pH (pH 2.0) appeared to be
partly reversible, as can be seen in Table 2. Upon reheating the protein,
a transition was observed, although with a lower enthalpy.
After a second reheating step again a transition could be observed.
These results also correspond with those described in literature, as
the denaturation of Ber e 1 at pH 2.0 was previously described to
be partly irreversible (Koppelman et al., 2004). At pH 7.0 the denaturation
of Ber e 1 appeared to be completely irreversible, as
reheating the samples did not show a transition (no further data
shown).