In this study, the molecular masses and isoelectric characteristics of pituitary LH and FSH in two species of callitrichid primate, the common marmoset (Callithrix jacchus) and the cotton-top tamarin (Saguinus oedipus), were determined. Comparative data for urine samples from Callithrix jacchus are also presented. The separation of gonadotrophins from pituitary extracts and urine was performed under nonreducing conditions using SDS\p=n-\PAGEand isoelectric focusing procedures. Hormone activity

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... n gel eluates was determined by in vitro bioassays for LH and FSH and by a microtitre plate enzymeimmunoassay for LH. The molecular masses of pituitary and urinary proteins were between 36 and 37 kDa for LH and FSH, and were similar in both species. A dimer form of pituitary LH with a molecular mass of 33 kDa was also found in the cotton-top tamarin, but not in the marmoset. Guanidine\p=n-\HCldissociation of gonadotrophins from marmoset and tamarin pituitaries before electrophoresis gave proteins of 16 and 28 kDa, and 16 and 25 kDa range, respectively. Isoelectric focusing revealed numerous peaks of bioactivity for both LH and FSH, indicating the presence of multiple molecular variants (isoforms) of each hormone. In both species pituitary FSH eluted over a narrower and more acidic pH range than LH. Isoelectric focusing profiles for pituitary and urinary LH in the marmoset were similar (pH range 5.0\p=n-\8.5), whereas urinary FSH demonstrated a more acidic profile than the pituitary protein. These results give comparative information on the properties of New World primate gonadotrophins, which should be useful in studies of their physiological action and in aiding the development of improved reagents and assays for their detection.