Figure 1 Conversion to enone (cross aldol condensation product) in the
reaction of acetone with p-formylbenzonitrile catalyzed by
albumin from different species. The biotransformations and their
analysis were conducted following reported protocols14.
Conversion is represented qualitatively in the figure by a cross, being
more significant in BSA and the lowest activity being observed in RSA
and PSA serum albumins.
As derived from Figure 2, it is interesting to note the shift between
Lys 199 and Arg 222 in HSA to the equivalent residues observed in BSA
(Arg 198 and Lys 221 according to BSA numeration). Apparently, those
replacements are conservative since both residues could be positively
charged at neutral pH. However, as will be described below, their pKas
are very different and could affect their role in catalyzing the
reaction. Also, in PSA, both equivalent positions are occupied by Arg.
Besides these replacements, the five seroalbumins showed catalytic
activity for the tested reaction (see Figure 1), confirming the
conservation of amino acid replacements.