The team compared two different kinds of bacteria ?one found in moderate environments and the other, an intense-heat lover. Both were photosynthetic (that is, using the sun's energy to create sugars for food). The focus of the research was a reaction that takes place in enzymes in the photosynthetic "reaction center" of the bacterial cell. While gradually raising the surrounding temperature, the scientists timed this reaction to see how reaction rates changed as things heated up.
A general rule for enzyme reactions states that as the heat rises, so does the reaction rate. Contrary to this rule, and the scientist's expectations, both reaction rates peaked at a certain point, and remained steady thereafter. For each enzyme, the peak occurred in the bacteria's "comfort zone." Further comparisons of the enzymes, which were nearly identical, turned up differences in just two of the hundreds of amino acids making up the enzyme sequence. When the scientists replaced these two amino acids in the enzyme adapted to the moderate temperatures with those of the heat-loving enzyme, they observed an increase of about 10 degrees in the average temperature at which the reaction rate peaked. Scherz: "This study shows that enzyme efficiency is tuned to the average temperature of the bacterial habitat, rather than the immediate conditions.
Source:American Committee for the Weizmann Institute of Science