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.