The insulin-like growth factor (IGF)-binding proteins (IGFBPs) are a family of six homologous proteins with high binding affinity for IGF-I and IGF-II. Information from NMR and mutagenesis studies is advancing knowledge of the key residues involved in these interactions. IGF binding may be modulated by IGFBP modifications, such as phosphorylation and proteolysis, and by cell or matrix association of the IGFBPs. All six IGFBPs have been shown to inhibit IGF action, but stimulatory effects have also been established for IGFBP-1, -3, and -5. These generally involve a decrease in IGFBP affinity and may require cell association of the IGFBP, but precise mechanisms are unknown. The same three IGFBPs have well established effects that are independent of type I IGF receptor signaling. IGFBP-1 exerts these effects by signaling through alpha(5)beta(1)-integrin, whereas IGFBP-3 and -5 may have specific cell-surface receptors with serine kinase activity. The regulation of cell sensitivity to inhibitory IGFBP signaling may play a role in the growth control of malignant cells.

We determined the proximate chemical composition as well as the construction costs of leaves of 27 species, grown at ambient and at a twice-ambient partial pressure of atmospberic CO2. Tbese species comprised wild and agricultural berbaceous plants as well as tree seedlings. Botb average responses across species and tbe range in response were considered. Expressed on a total dry weigbt basis, tbe main cbange in cbemical composition due to CO2 was tbe accumulation of total non-structural carbobydrates (TNC). To a lesser extent, decreases were found for organic N compounds and minerals. Hardly any cbange was observed for total structural carbobydrates (cellulose plus bemicellulose), lignin and lipids. Wben expressed on a TNC-free basis, decreases in organic N compounds and minerals were still present. On tbis basis, tbere was also an increase in tbe concentration of soluble pbenolics.In terms of glucose required for biosynthesis, tbe increase in costs for one cbemical compound -TNCwas balanced by a decrease in tbe costs for organic N compounds. Tberefore, tbe construction costs, tbe total amount of glucose required to produce 1 g of leaf, were ratber similar for tbe two CO2 treatments; on average a small decrease of 3% was found. Tbis decrease was attributable to a decrease of up to 30% in tbe growtb respiration coefficient, tbe total CO2 respired [mainly for N AD(P)H and ATP] in tbe process of constructing 1 g of biomass. Tbe main reasons for tbis reduction were tbe decrease in organic N compounds and tbe increase in TNC.

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