No abstract

S J nopsisThe conformational transition of poly->tyrosine in 0.lM KC1 was investigat,ed by OR11 and infrared spectroscopy, potentiometric titration, and sedimentation velocity experiments. I t is shown that the fully ordered conformer is obtained by slow titration of the random coilwith 0.1N HC1 at 25°C. The charge-induced transition, at variance with other poly-a-amino acids, is completed in a narrow range of a. A n aggregation process was detected both by potentiometric titration and sedimentation velocity. The polyamino acid aggregates around a = 0.7 at 25°C when the conformational transition is almost complete. Infrared spectra, in the region of the amide I band (1650 cm-1) showed that the t,ransition is a random coil --f antiparallel p one. Evidence exists t,hat the form is of the intramolecular type. The foregoing interpretations of ORI) and C1) spectra in terms of the a-helix conformation are discussed.

Density of natural and experimental populations fluctuates. Oscillations may depend either from dmsity-independent mechanisms, or from densitg-dependent mechanisms.