Detection of erythrocyte membrane protein alterations in hereditary spherocytosis through the use of thermal stress: a spin label study

A spin-label study of membrane proteins and internal microviscosity of erythrocytes in hereditary spherocytosis

Electron spin resonance (ESR) spectra of erythrocyte membranes of patients with hereditary spherocytosis (HS) and of healthy controls labeled with a maleimide spin label did not differ significantly both before and after prolonged incubation at 37 degrees C. It suggests that the different behavior of spin-labeled HS erythrocyte membranes upon incubation at a higher temperature reported previously is due indeed to structural abnormalities of HS red cell membranes and not to alterations in their proteolytic activity. Measurements of the rotational correlation time of Tempamine spin probe demonstrated a significant elevation of internal microviscosity of erythrocytes in HS, more pronounced in non-splenectomized patients.

Effect of proteolysis on the electron spin resonance spectra of maleimide spin labeled erythrocyte membrane

The ratio of low-field amplitudes of weakly and strongly immobilized signals of ESR spectra of a maleimide spin label bound to erythrocyte membranes (hw/hs) increases progressively during incubation at 37 degrees C. This increase is due to the 'self-digestion' of membrane proteins by endogenous proteinases and is attenuated by proteinase inhibitors. Digestion of membranes with chymotrypsin also increases the hw/hs ratio. These results suggest a need for a careful interpretation of data from spin-labeled membrane proteins, especially in experiments involving prolonged incubations of membrane preparations when the proteolytic effects may be significant.

Saturation transfer EPR studies of membrane alteration in hereditary spherocytosis

Our earlier spin label electron paramagnetic resonance (EPR) studies of hereditary spherocytosis (HS) erythrocyte revealed the existence of structural alteration(s) when the membrane is subjected to heat stress. We have now used saturation transfer EPR to show restricted motion in membrane proteins even without subjecting membrane to stress. The abnormal motional behavior is amplified when membranes are incubated at 47 degrees C and is readily detectable by conventional EPR. Gel electrophoresis and lipid assays show that proteins but not lipids are released upon heating. Thus, the more restricted motions in HS membranes may be due to a different membrane protein organization, ultimately resulting in the abnormal morphology of HS cells.