This study was undertaken to characterize further the growth hormone dependent plasma factors which stimulate sulphate uptake (PSF) and thymidine incorporation (PTF) in cartilage segments from hypophysectomized rats. An assay system utilizing labelling with 35SO4 and 3H-methyl-thymidine was devised to measure both types of activity simultaneously and to determine whether these activities run in parallel during chemical fractionation procedures. Acromegalic plasma stimulated sulphate and thymidine uptake as much as 18 × and 30 × respectively above the uptake of the basal medium. Activity measurements were not rigidly quantitative due to high variances, especially in PTF measurements. Both activities in acromegalic plasma were thermo-labile at 80°C for 30 minutes. PSF was stable from pH 2–pH 10. PTF was possibly partially inactivated at pH 2. Digestion with pronase destroyed PSF and probably PTF. Acromegalic plasma was fractionated by graded ethanol precipitation, ion exchange chromatography, starch gel electrophoresis, and molecular sieving through Sephadex (G-100, G-200). PSF and PTF activities run in parallel throughout these procedures. These findings suggest that the active material is associated with a peptide with a molecular weight between 9500 and 35 000, which is more positively charged than many other plasma proteins.
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Brande et al. (1971) studied this question.