Silvia Morante

[21] Magnetic susceptibility of hemoglobins

Publisher Summary This chapter discusses the magnetic susceptibility of hemoglobins. In principle, the diamagnetic susceptibility of a molecule is linked to its average electronic density and should be sensitive to the structural properties and molecular volume of the protein. The interpretations of the diamagnetism of a large molecule in terms of Pascal constants and bond properties are precise only at a 10% level, while an inspection of systems where cooperative bond breaking occurs—such as water at melting or where dramatic conformational changes affect the structure, such as rhodopsin—reveals that changes of no more than few percent should be expected in the diamagnetism. Moreover, in hemoglobins, any spin change at the heme that may occur in response to conformational transitions will usually overwhelm these small effects on diamagnetism. A variety of instruments have been used for magnetic susceptibility studies on hemoglobin. Basically they are of two types: balances based on force methods and fluxmeters based on superconducting circuitry.

Superconducting susceptometer for high‐accuracy routine operation

We present a new version of a SQUID susceptometer with the following performance. The overall accuracy is δχ≃3×10−9 (SI units). Within this figure is allowed the reproducibility in interchanging samples, the thermal expansion of the samples up to 10%, and the constancy of the calibration over a time scale of months. The sample can be interchanged in minutes and the overall time taken by the actual measurement procedure, to give results within the accuracy quoted above, is of the order of 5 min for one sample at one temperature. The temperature regulation is precise within 0.2 K between 40 and 300; the accuracy in the sample temperature has been tested to be within 0.5 K in the room temperature range. This performance is of great relevance for studies of biological molecules in solution, when different samples in different solution conditions must be compared with accuracies better than parts in a thousand of the magnetic susceptibility of the solution.

Interaction of hexacyanoferrate (III) with some copper (II) complexes

Abstract The interaction between hexacyanoferrate(III) and some copper complexes of different geometry was studied. In solution, and in the presence of coordination unsaturation of copper, 1:1 and 2:1 Cu:Fe adducts formed and were characterized by the absence of any copper electron paramagnetic resonance (EPR) signal. The magnetic susceptibility of the 1:1 adducts is essentially equal to the sum of those due to the parent compounds. Solid state studies confirm the solution data. In the light of the present results the absence of the EPR signal of [Fe(CN) 6 ] 3− -treated galactose oxidase is discussed.

X-Ray Iron K Edge of Human Hemoglobins

The development of the synchrotron radiation sources allows now to extend x-ray absorption spectroscopy to aqueous solutions of biological molecules. Preliminary unpublished results by Yuen et al.[1] reported an energy shift of the K edge of about 5 eV going from the deoxy to ligated derivatives of hemoglobin. Stimulated by this finding we have undertaken a more extensive study of the K-edge absorption spectra for several derivatives of human HbA.

The use of a superconducting magnetometer to measure spin equilibria in hemoglobin

Abstract We are very glad to have the opportunity to outline the outcome of so many years of happy collaboration in this volume to honour Prof. Giorgia Careri. Indeed it is quite appropriate to do so. Even if the reader will not find referenced any paper in collaboration with him, still his role in this work has been just as great and relevant. It is thanks to Prof. Careri that one of us (M.C.) was at first introduced to the world of superfluidity and superconductivity and then to biophysics. Superconducting electronics, with SQUIDs etc., was offering good opportunities for the developement of susceptometers sensitive and accurate enough for biological studies. The first such efforts were carried out in Jim Mercereaus laboratory in Caltech by E. Hoenig and Run Han Wang. One of the authors, M.C., following the style of Careris laboratory, had the opportunity to spend one year doing research abroad in an outstanding laboratory. As he had been using SQUIDs for high resolution magnetic studies in solid state physics and wantend to expand his studies to biological matter, he chose to go to Caltech, where he also developed his interest in hemoglobin. Afterwards, in Careris laboratories in Rome and Monterotondo, SQUID susceptometers were developed, with which the authors carried out the first experiment on ferric hemoglobin with Max Perutz. These studies have been pursued up to the present, even after M.C.s laboratory moved to Trento. Therefore, we would like to thank Prof. Giorgio Careri for creating the opportunity by which we have been able to enjoy this collaboration for all these years.

Complexes of copper(II) dipeptides with hexacyanoferrate(III). Magnetic and spectroscopic properties

Abstract The interaction between hexacyanoferrate(III) and two copper(II) dipeptide complexes, such as Cu(II)- glycylhistidine and Cu(II)-glycylphenylalanine, has been investigated by electronic and EPR spectroscopy and by magnetic susceptibility measurements. In both cases the magnetic susceptibility values sum to those corresponding to the patent complexes. However, the electronic relaxation time of the copper(II) ion in the mixed complexes is modified so much that the copper(II) EPR signal disappears suggesting the existence of a specific metal—metal interaction probably through a cyanide bridge. This hypothesis is also supported by the appearance of an hypsochromic shift of the Cu(II) electronic band after addition of hexacyanoferrate(III).

Magnetic Properties and Structure of Oxyhemoglobin and Carbonmonoxyhemoglobin

The case is presented about the magnetic state of HbO2 and HbCO to show, on the basis of available experimental data, that the controversy on the possible presence of unpaired spins in the iron-ligand complex is not yet resolved. We point out the need for the identification of a fully diamagnetic state of the protein to be taken as reference and outline a possible method. A few preliminary results on packed red cells are presented.