Maltose-binding protein reactions

New ways of controlling enzyme function can also be introduced. Natural enzymes often exhibit some form of posttransla-tional regulation that affects their activity, which could take the form of interaction with a small molecule to enhance or inhibit activity in a particular environment. The maltose-binding protein can function as a switch when inserted into a gene such as fS-lactamase (50), which enables a level of control over the desired reaction, based on the presence or absence of a molecule such as maltose. 

In contrast D for lactate in the cytoplasm of Escherichia coli is about 10 cm s (131), and its diffusion-controlled limit (with respect to itself) is computed to be 10 M s . Thus, the diffusion limit is three orders of magnitude smaller for this small molecule within the cell as compared to water. The first important conclusion of this analysis is that bimolecular reactions between small molecules are slowed considerably in the crowded conditions of a cell. Consequently, unimolecular reaction mechanisms that might not be kinetically competent (or even observed) in the laboratory could be feasible in the confines of a cell. Consider now a protein within the cytoplasm. For example, D for maltose-binding protein (72kDa) is 10 in the cytoplasm and 10 in the periplasm of E. coli. (133). Within the periplasm, the diflfusion-hmited rate constant between two maltosebinding proteins is approximated by... 

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