Mammary explants from pregnant mice cultured in the presence of lactogenic hormones express their differentiated function by producing milk components in vitro. In the present paper radioactive calcium uptake was studied in the mammary gland during terminal differentiation, when lactogenesis was initiated. Under these conditions a relevant accumulation of calcium in the tissue was clearly demonstrable. We have characterized the calcium uptake by the tissue as a saturable and energy dependent process. When 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], the major calcium regulator hormone, was added to the incubation medium the secosteroid strongly stimulated this process by increasing the maximal velocity without significantly altering the Michaelis Menten constant (Km). Detectable increases in calcium uptake could be measured after the explants were cultured with 1,25-(OH)2D3 for 30 min, with the response continuing to increase sharply over time and reaching a plateau at 3 h. The increase was not affected ...

1,25-Dihydroxycholecalciferol-dependent calcium uptake by mouse mammary gland in culture.

The general features of [14C]spermidine binding to plasmalemma vesicles isolated from zucchini (Cucurbita pepo L.) etiolated hypocotyls are reported in the present paper. The specific interaction of the polyamine with the plasma membranes was reversible and thermolabile, since it decreased by about 50% in the assay performed at 40[deg]C compared to that carried out on ice. On the contrary, nonspecific binding was unaffected by temperature. Specific spermidine binding showed a pH dependence with a maximum at pH 8.0 and it reached saturation between 0.75 and 1 mM external spermidine concentration. The value of the dissociation constant calculated from Scatchard analysis was 4.4 x 10–5 M. Specific spermidine interaction appeared to be sensitive to detergents and was markedly reduced by the presence of divalent cations, such as Mg2+ and Ca2+, whereas it was stimulated by monovalent cations. Polyamine binding sites were highly sensitive to pronase treatment. Competition experiments, performed using a series of compounds structurally related to spermidine, may provide some indication of the characteristics of spermidine binding sites. The results presented here suggest that specific spermidine binding occurs mainly with the protein component of the plasma membrane.

Polyamine Binding to Plasma Membrane Vesicles Isolated from Zucchini Hypocotyls

1α, 25-dihydroxycholecalciferol and human histiocytic lymphoma cell line (U-937): The presence of receptor and inhibition of proliferation

Evidence for a 1,25-dihydroxycholecalciferol-dependent spermine-binding protein in chick duodenal mucosa.

Effect of spermine on association of protein kinase C with phospholipid visicles

Polyamine binding by a cytoplasmic factor in the duodenal mucosa of new-born chick

Chick duodenum contains proteins capable to bind radioactive spermine and calcium. From competition studies the spermine binding protein(s) seem(s) to differ from calcium binding protein. This finding makes possible to distinguish and assay separately those two cation binding activities.

Discrimination between spermine and calcium binding activities in crude extracts from chick duodenal mucosa

Human peripheral lymphocytes contain a cytosolic factor able to bind noncovalently spermine with high affinity. Other polyamines bind much less effectively and the order is: spermidine, putrescine, cadaverine. The factor is heat sensitive, and appears to be a protein on the basis of nucleolytic and proteolytic digestion. It seems to be an intracellular specific binder for spermine.

G. Capone

Papers

Polyamine binding by a cytoplasmic factor in the duodenal mucosa of new-born chick

Discrimination between spermine and calcium binding activities in crude extracts from chick duodenal mucosa

Heat-Sensitive Spermine-Binding Factor from Peripheral Human Lymphocyte: