Circular dichroism studies of sheep β-lipotropic hormone

Abstract

The far ultraviolet circular dichroism spectra of sheep β-lipotropic hormone (β-LPH) were recorded under different conditions of pH, temperature, salt concentration, and solvent composition. Results confirm the stability of the hormone in strong basic or acidic solutions; moreover, temperatures up to 50 °C do not seem to affect noticeably the conformation of β-LPH. However, increasing the NaCl concentration or addition of dioxane in the solution brings about a conformational transition of the chain, interpreted as an increase in the helical content. The method of Yang (Chen, Y. H., Yang, J. T. &Martinez, H. M. (1972) Biochemistry 11, 4120–4131) was used to compute the proportion of helical, β, and unordered forms of the hormone chain. The proportions are compared with those obtained from Fasman's predictive method (Chou, P. Y. &Fasman, G. D. (1974) Biochemistry 13, 211–221 and Chou, P. Y. &Fasman, G. D. (1974) Biochemistry 13, 222–245) based on the known amino acid sequence of β-LPH.