Possible evidence for the existence of a growth hormone fragment in porcine pituitary.

In an attempt to search for growth hormone fragments in the pituitary, a radioimmunoassay was developed for a 55 residue S-amino-ethylated CNBr fragment (fragment B) of porcine growth hormone corresponding to residues 126-180 of human growth hormone. The assay was sensitive to 50 pg of fragment B whereas displacement of 125I-labelled fragment B by procine growth hormone required a 10(3) M excess and was non-parallel. In a homogolous porcine growth hormone radioimmunoassay, fragment B was non-reactive. Gel filtration of an extract of porcine pituitary on Sephadex G-75 revealed three peaks of fragment B immunoreactivity: peak I (29% of total immunoreactivity) eluted in the void volume, peak II (49%) eluted in the position of growth hormone, and peak III (12%) was more retarded than fragment B. Nearly all of the growth hormone immunoreactivity eluted as a single peak in the position of 125I-labelled porcine growth hormone. The dilution curve of peak III but not of peaks I or II was parallel to that of fragment B. The results indicate the existence within porcine pituitary of material cross-reactive with a portion of the growth hormone molecule, possible representing a growth hormone fragment.