Membrane-bound adenylate cyclase from rat brain has been solubilized with Lubrol-PX. The soluble enzyme is nonsedimentable at 165,000g for 2 hr, is filterable through 0.22 /x Millipore filters and is responsive to F_. The solubilized adenylate cyclase has been stabilized for at least 7 days by the addition of 5 mM NaF and 5 mM MgS04. The enzyme has an estimated molecular weight of 800,000 which was obtained on the basis of a calibrated Bio-Gel A-15 m (agarose) column. The enzyme has been purified 18-fold representing the removal of over 99% of the starting protein. Addition of fractions removed during purification did not increase enzyme activity. The partially purified adenylate cyclase has ATPase and adenosine 3',5'-cyclic monophosphate phospho-A L Vdenylate cyclase catalyzes the conversion of adenosine triphosphate to cAMP,* 1 and plays a pivotal role in mediating the effects of a wide variety of hormones (Sutherland et cil., 1965). The physiological importance of adenylate cyclase has long been recognized and its properties as a particulate, hormone-responsive membrane-associated enzyme have been extensively described and are the subject of investigation (

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)

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A differential centrifugation technique, in which all extracellular water except that intimately associated with the cell (pericellular domain) is removed, has been applied to isolated Novikoff hepatoma cells. The pericellular volumes accessible to albumin, inulin, raffinose, and sucrose were inversely related to the molecular weights of the test solutes. This phenomenon was not detectable in erythrocytes or in fat cells. Selective removal of cell surface components by enzymatic treatment produced proportional changes in the relative volumes of distribution accessible to the solutes. This discrimination in the volume accessible to each of the solutes is analogous to that obtained in gel chromatographic separation and represents, in effect, excluded volumes which are inversely related to solute size. This exclusion is associated with components of the Novikoff cell surface, including the surface coat and the microvilli that cover the Novikoff cell. These structures provide an additional level of discrimination for the Novikoff cell not seen in certain other cell types.

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