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: (14C)-glucose uptake, its oxidation to CO2 and incorporation into glyceride-glycerol, glycerol release, and (14C)- 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 µg/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. (Endocrinology87: 900, 1970)
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Swislocki et al. (1970) studied this question.