Reappraisal of the electron spin resonance spectra of maleimide and iodoacetamide spin labels in erythrocyte ghosts.

The effects of sulfhydryl inhibitors (iodoacetamide and N-ethylmaleimide) on the electron spin resonance spectra of two maleimide and two iodoacetamide spin labels in erythrocyte ghosts were found to correlate with their relative “lipid”/water partition coefficients. But the spectral characteristics of the maleimide spin labels, and their ghost concentrations after iodoacetamide inhibition, are not consistent with the hypothesis that interprets their spectra solely on the basis of a heterogenous membrane distribution. An alternative hypothesis is suggested which is compatible with relative “lipid solubilities” and the iodoacetamide inhibition spectra.