Chelating agents sites accessibility 284

Table 1. Sites accessible to various types of chelating agents Chelating agent type Accessible sites...

Some of the disagreement in the metal binding work may arise from uncertainties as to whether binding was controlled by kinetics or thermodynamics. To illustrate what is meant, consider the addition of one zinc ion to apoenzyme. Is the site where this zinc ion is bound the most stable site or the one most accessible Evidently this might depend upon the time, and whether or not the concentration of zinc is controlled by a chelating agent. 

Iron chelators (type 2) are of medical interest as agents that can block cell proliferation. To what extent this is due to interference with RNR is not well understood. However, recent experiments on the isolated proteins show that an agent such as desferrioxamine can destroy the radical and chelates iron from the active form of the HSVl protein 111), whereas it has no direct effect on the tyrosyl radical of mouse R2 112). However, it seems that the iron in the dinuclear sites without neighboring tyrosyl radical is accessible to desferrioxamine complex-ation in mouse as well as HSVl R2, again suggesting a structural difference between iron sites with and without a neighboring radical. 

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