Haemoglobin Conformational changes

Even though the iron atoms are separated in haemoglobin by about 25 A, communication between them is still able to occur and this has been postulated to involve a trigger mechanism (Perutz, 1971). The trigger is the movement of the proximal histidine as dioxygen binds to (or is released from) the Fe(n) and results in interconversion between the T and R structures. This movement causes a conformational change which is transmitted through the protein to the other iron sites. X-ray studies indicate that relative shifts of up to 6 A at subunit interfaces occur between the T and R states (Perutz, 1978). 

Thus, in the anaerobic response the plant haemoglobin protein present in the roots could assume different conformations depending upon the oxygen concentration. This conformational change could activate another molecule which in turn could alter transcription factor binding and induce the anaerobic response (Fig. 6). 

Blumenfeld, L.A., R.M. Davydov, S.M. Magonov, and R.O. Vilu (1974). Studies on the conformational changes of metalloproteins induced by electrons in water-ethylene glycol solutions at low temperatures. Haemoglobin. FEBS Lett. 49, 246-248. 

Neutron experiments were first made on haemoglobin [98,99,147,166,167] and were extended to myoglobin [44,168], lysozyme [169] and catalase [170] as models of typical globular proteins. In parallel with X-ray scattering, the haemoglobin work (mainly in H20) identified a conformational change between the oxy- and deoxy-forms which was reflected in an difference of 0.054 nm in H20 buffers. Scattering curve comparisons to <2 = 3 nm with the crystal structures verified this. 

FIG. 13.2 D iagram of conformational change in tertiary structure of the haemoglobin sub-units on reaction with oxygen. (Perutz, 1970, modified in correspondence.)... 

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