Spin-label studies of membrane-associated denatured hemoglobin in normal and sickle cells

An ESR study of pathologic red blood cell membranes (RBCM)

A comparative study of red blood cell membranes from normal subjects and beta-thalassemia and sickle cell anemia patients was performed by spin labeling at the lipidic and protein phase. The results show that the quantity of bound spin label is the same for sickle, thalassemic, and normal membranes. The data from 5-doxyl stearic acid suggest an increase in fluidity for the thalassemic membrane.

A spin label study of the ionic strength dependent conformational change in the human Ia molecule

Purified human Ia molecules were labelled with maleimide or isothiocyanate spin labels or by reacting "TEMPAMINE" spin label with the neuraminic acid of their carbohydrate residues. It was found that increasing the ionic strength from 0.05 to 0.75 markedly increased the dipolar interaction between the maleimide-attached labels, but no effect was found of ionic strength or motion on dipolar interaction with the other two labels. The effect of increasing ionic strength could be blocked by the prior addition of Ia-specific antibody, but could not be reversed by the addition of antibody after ionic strength was increased. These findings complement an earlier finding that increasing ionic strength over the range 0.05-0.75 has an inhibitory effect on the combination of Ia with its antibody. Because the maleimide spin labels attach predominantly to SH groups it is suggested that increasing ionic strength causes conformational changes in the immunoglobulin loop region which alter the accessibility of the Ia antibody-binding site.

Interaction of superoxide dismutase with phospholipid liposomes. An uptake, spin label and calorimetric study

The effect of superoxide dismutases from five species upon phospholipid bilayers has been investigated. The uptake by egg phosphatidylcholine bilayers of the holo and apo forms of bovine superoxide dismutase increases with enzyme concentration and only a fraction of each is removed by treatment with trypsin. These uptake data indicate that both forms of the enzyme associate with and are embedded within lipid bilayers. From the spectrum of the spin label 2-(3-carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxyl, the binding of superoxide dismutase to egg phosphatidylcholine bilayers can be shown to disorder the lipid packing. The disordering by the bovine holoenzyme is small but increases with increasing enzyme concentration and period of incubation. The disordering effects of the apoenzyme are much larger and are reversible by Cu2+, Zn2+ reconstitution of the apoenzyme. The disordering effect of the apoenzyme is further confirmed by differential scanning calorimetry. The gel to liquid crystalline phase transition of egg phosphatidylcholine is lowered 7 degrees C by 25% by weight apo-superoxide dismutase to lipid. Human, dog, swordfish and yeast superoxide dismutases also disorder, and to a greater extent than the bovine enzyme. The greatest perturbation is produced by yeast superoxide dismutase; a 20% decrease in the order parameter by 50% by weight enzyme to lipid.