Evaluation of Hen Egg White as a Model of Cytoplasmic Pumping Mechanisms
Cameron, I1,*; Fullerton, G2
Key Words: Hen egg white, albumen structure, gel-sol, proton NMR, polarization microscopy, water
Received 16 May 2010; revised 29 July; accepted 14 August. Published 27 August 2010; available online 27 August 2010
Summary
The most widely taught explanation of non-homogeneous distributions of cellular metabolites and ions relies on molecular pumps residing in cellular membranes. This study uses fresh hen egg white to demonstrate the capacity of hen egg white to manipulate rheological properties that correlate with co-solute distribution changes previously attributed solely to active (energy consuming) membrane pumps. When egg white was placed on a sieve a thin sol albumen fraction flowed through the sieve and a thick gel albumen fraction was obtained from the sieve surface. The thick gel, but not the thin albumen sol fraction, excludes a low molecular weight dye, methylene blue. The two fractions were examined by polarization microscopy and their water proton NMR T1 and T2 relaxation times were measured. Thick gel was composed of elongated birefringent domains rich in microscopic particles. The thin albumen sol had no such domains, fewer particles and does not exclude dye. Gel agitation fragments the gel domains and frees their particles concomitant with conversion to a sol, and with loss of the dye exclusion property. The gel to sol conversion caused shortening of the NMR T1 relaxation time consistent with increased freedom of motion of water attached to proteins previously entrapped in the less mobile gel. Thus water in the gel differs from bulk water in both motional and dye exclusion properties.