Molecular Weight of Sheep Pituitary Interstitial Cell-stimulating Hormone

Abstract

Two new procedures for the isolation of interstitial cell-stimulating hormone (ICSH) from sheep pituitary glands have been described in recent years^1,2. Sedimentation coefficients (s_20°,w) of the hormone were reported to be 2.47 in phosphate buffer¹ of pH 6.8 and 2.32 S in glycine buffer² of pH 6.0. From these values, together with values for the diffusion coefficient and partial specific volume, these authors^1,2 computed the molecular weight of ICSH to be 28,000–30,000. We have recently re-examined the sedimentation behaviour of ovine ICSH and found that the molecular weight of the hormone changes with the pH of the buffer. Results also indicate that the ICSH molecule forms reversible aggregates. We wish to report herein the molecular weight of the ICSH monomer.