The Molecular Properties of Human Chorionic Somatomammotropin
Salvatore Aloj 1 and Harold Edelhoch 1
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1 From the Clinical Endocrinology Branch, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland 20014
The helical content of human chorionic somatomammotropin has been determined by circular dichroism measurements in the far ultraviolet. Only small changes in circular dichroic activity occur between pH 2 and 12 in aqueous solution. An important modification in tertiary structure, however, takes place below pH 4 which has been followed by changes in tryptophan and tryosine absorption and emission intensities. A structural transition occurs also in alkali above pH 10 which has been detected by the increase in quantum yields of the tryptophanyl and dimethylaminonaphthalene sulfonyl chromophores.
The conformational transitions produced by urea at pH 5.0 and 8.0 in human chorionic somatomammotropin have been evaluated by circular dichroism, absorption, and fluorescence measurements. Although minor differences in properties and stability exist between human chorionic somatomammotropin and bovine growth hormone or ovine prolactin, the composite behavior of human chorionic somatomammotropin resembles the latter two proteins sufficiently closely to suggest that there is an important degree of structural similarity between all three molecules.
Submitted on March 5, 1971
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