In VitroMetabolic Effects of Bovine Growth Hormone Fragments in Adipose Tissue

Abstract

A limited tryptic digest of bovine growth hormone, which dissociated in 50 % acetic acid into 2 fragments of 16,000 and 5000 molecular weight, was evaluated for bovine growth hormone (BGH) activity in rat adipose tissue in vitro. Both fragments, whether tested individually or as mixtures in equimolar ratio, possessed the several in vitro metabolic activities commonly associated with native BGH: ( 14 C)-glucose uptake, its oxidation to CO2 and incorporation into glyceride-glycerol, glycerol release, and ( U C)-histidine incorporation into adipose tissue protein. The fragments, which also possess growthpromoting activity, were effective in vitro on most parameters of BGH action at concentrations of 25 jug/ml medium. At a 10-fold increase in concentration all the several parameters of BGH which were evaluated became manifest. These results indicate that while the 2 fragments of the tryptic digest of bovine growth hormone obtained are considerably less potent than native BGH they nonetheless possess BGH activity both in vivo and in vitro. Moreover, these data demonstrate that various metabolic effects of BGH are not dissociable by limited tryptic fragmentation of the BGH molecule since each of the 2 fragments of different primary structure exerted similar metabolic effects. These studies suggest that there may be more than one active site in growth hormone. (Endocrinology 87: 900, 1970)

Conformational Changes Required in the Human Growth Hormone Receptor for Growth Hormone Signaling

“…As also described for FDC-P1 cells transfected with a hybrid of the hGHR extracellular domain linked to the murine granulocyte/macrophage-CSF receptor transmembrane and intracellular domains (16), hGH120R cannot induce Ba/F3(8/6) or IM9 cell proliferation (34,36). This was originally attributed to nonformation of the "active" hGH⅐(hGHR) 2 complex, but recent data show that hGHG120R dimerizes and internalizes the GHR as well as does GH (37). GHR05 binding does not increase in Ba/F3(8/6) cells incubated with hGHG120R, in contrast to its behavior with native hGH.…”

“…To analyze the possible relationship between the GHR05 binding increase and hGH-induced receptor conformational change, an hGH mutant (hGHG120R) was employed that is able to bind the hGHR but not to form the active hGH⅐(hGHR) 2 complex. hGHG120R has a Gly 120 3 Arg mutation affecting the second GH binding site, which impedes correct receptor dimerization and subsequent proliferation induction (33).…”

“…1 essential for normal growth and development, induces a variety of biological effects including linear growth, lactation, nitrogen retention, diabetogenic and insulin-like effects, and macrophage activation (1)(2)(3)(4). Each of these effects is initiated by hGH interaction with specific cell receptors.…”

“…In contrast, the hGHBP is univalent, as it uses the same amino acids to bind either hGH site I or site II. An hGH excess dissociates the hGH⅐(hGHBP) 2 complex to form a monomeric complex. Biological response triggering requires sequential binding of the first receptor subunit to site I on a GH molecule, followed by binding of the second receptor to GH site II, forming the GH⅐(GHR) 2 complex (16).…”

Spin-Label Studies of Bovine Growth Hormone and Its Active Fragment

“…This suggests that the segment 96-133 of bGH represents the amino acid sequence requisite for growth hormone activity. 2,5,8) Physico-chemical properties of A-II have been investigated by circular dichroism and fluorescence emission spectroscopy.8-10) Gel filtration analyses and difference spectrum measurements revealed that a tyrosine residue in A-II was exposed on the surface of the fragment molecule existing in the monomer form and was held between the fragment molecules under the conditions where A-II existed as dimer and trimer. 11) To further elucidate the structure-function relationship of bGH in the present study, confonnations of A-II and its parent molecule, bGH, were t This work was supported in part by grants for scientific research from the Ministry of Education, Science and Culture of Japan.…”