Monday, September 20, 2010
In early biochemistry subjects proteins (enzymes) are described as catalytic switches. With their on/off modes corresponding to whether they are occupied by a substrate or unoccupied. The conformation of the protein was suited to find its one specific substrate, and accordingly the substrates would fit into the protein like a key into a lock. This ‘lock and key’ mechanism implies that the protein would be held in the static ‘lock’ conformation waiting for its substrate.
However when considering the Boltzmann distribution it seems unlikely that a protein (consisting of many individual molecules) could remain in a fixed position. In fact it is known that proteins can exist in many different structures and depend on many different parameters outside of their substrates. But if proteins can have a vast number of conformations how do they perform their highly specific functions? Section 9.6.3 of the text gives an interesting viewpoint: within a bulk sample of the myoglobin protein there are many different ‘conformational substates’ (shown by R. Austins experiment, figure 9.13). These substates are able to perform the overall protein function of binding oxygen, but they each have slightly different binding affinities due to their structural differences. Thus proteins are able to satisfy the Boltzmann distribution while still maintaining their function. However in regard to the lock and key fit, proteins are not so easily typified. In this context the proteins would be more aptly described as the lockpicker’s toolkit.
Posted by Heather at 11:51 PM