The Self-Diffusion Coefficients of Myoglobin and Hemoglobin in Concentrated Solutions

This is the authors' abstract. We don't add key points for this paper.

The self-diffusion coefficients of myoglobin and hemoglobin have been determined with a modification of the Northrup-Anson procedure in which diffusion is made to occur through a Millipore filter paper. In solutions less concentrated than 6 mm (heme) or about 10% (w/v), the self-diffusion coefficient is found independent of protein concentration. At greater protein concentration the logarithm of the self-diffusion coefficient falls linearly with increasing protein concentration. The decrease in self-diffusion coefficient is most simply related to the volume fraction of the solution occupied by protein. The relation between self-diffusion coefficient and hemoglobin concentration remains continuous and linear to the highest attainable concentration, which is the concentration within the erythrocyte. At this concentration the hemoglobin molecules are close-packed and nearly contiguous. The self-diffusion coefficient of hemoglobin in this environment is only 10-fold less than that at infinite dilution. This and other findings indicate that frictional interactions between myoglobin or hemoglobin molecules are minimal. The numerical values of the self-diffusion coefficient serve to test the molecular mechanism proposed for myoglobin (or hemoglobin)-facilitated oxygen diffusion. The facilitated oxygen flux per unit protein concentration is found to be directly proportional to the protein self-diffusion coefficient, as predicted.