The Properties of Bovine Growth Hormone

I. BEHAVIOR IN ACID SOLUTION

From the ¹ From the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland 20014

1. The effect of acidification on the fluorescence, absorption, viscosity, sedimentation, optical rotatory dispersion, and polarization of fluorescence of bovine growth hormone has been measured. All the data are consistent with a molecular transition that results in increased unfolding of the hormone as the pH is reduced from 5 to 2. A pK of 3.55 and a hydrogen ion dependence of 1.5 have been determined from the increase in fluorescence that accompanies the molecular transition.

2. Although major changes occur in all the properties studied, the helical content, as determined either from the Moffitt or Schechter-Blout equations, remains the same. Apparently major modifications in tertiary structure can occur independently of those in secondary structure.

3. A second transition in the neutral pH range has been observed by polarization of fluorescence measurements.

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