  A careful analysis of measurements of circular dichroism of poly(L-glutamic
acid) (PGA) shows that the data can be very accurately described by introducing
a third state for the PGA configuration, in addition to the helix and coil
ones, and considering a simple equilibrium between these three states, without
cooperativity. The third state is more conspicuous when high molecular weight
polyethyleneglycol (PEG) is added. Excluded volume effects shown by differences
in presence of short and long PEG chains indicate a direct interaction of PEG
and PGA rather than an osmotic effect.
