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This paper shows how bubbling the reaction medium with CO affects the nucleation/growth of Pt nanoparticles under the synthesis using formic acid or formaldehyde as reducing agents. CO has been found to affect not only the dynamics of the Pt(IV) to Ptx0transformation but also the size of the formed particles (1.1–3.9 nm) deposited on the carbon support (ca. 20 wt% Pt). The dual role of CO due to combining the functions of a stabilizer and a reducing agent has been shown. The study demonstrates that the introduction of the dispersed carbon support to the reaction medium leads to the enhancement of the CO positive effect on the microstructure of Pt/C catalysts. In this case, the spatial distribution of Pt nanoparticles over the carbon support surface becomes more uniform that is conducive to increasing the electrochemical surface area. Thus, CO is a unique reagent used to control the microstructure of Pt nanoparticles during their wet synthesis.

The function of cell surface-associated insulin-like growth factor-binding proteins (IGFBPs) is controversial. Both inhibition and facilitation of IGF action as well as IGF-independent effects have been reported. We examined the influence of endogenous cell surface-associated IGFBPs on IGF-I receptor (IGF-IR) function in Ishikawa endometrial cancer cells by comparing the effects of IGF-I and its truncated analog des-(1-3)-IGF-I on several components of the IGF-IR signal transduction pathway in the absence of significant amounts of soluble IGFBPs. IGF-I and des-(1-3)-IGF-I are known to have similar affinities for IGF-IR, although the affinity of des-(1-3)-IGF-I for IGFBPs is greatly reduced. Here we show that the two ligands were equipotent not only in IGF-IR binding but also in receptor activation in NIH 3T3 cells overexpressing IGF-IR and possessing a relatively small number of cell surface-associated IGFBPs. In contrast, des-(1-3)-IGF-I manifested a remarkably higher potency as compared with IGF-I in inducing short and middle term cellular responses in IGF-IR-transfected Ishikawa endometrial cancer cells possessing a high number of both the receptor and the cell membrane-bound IGFBP-3. Thus, this difference in the effects of IGF-I and des-(1-3)-IGF-I can be attributed to the attenuation of IGF-I-mediated IGF-IR signaling by membrane-bound IGFBP-3.

Detergent-mediated activation of the phagocyte superoxide-generating NADPH oxidase requires the participation of at least four proteins: the membrane-bound heterodimeric cytochrome b558 and three cytosolic components, p47-phox, p67-phox and a Rac1/Rac2 protein. Peptides corresponding to sequences of different subunits of NADPH oxidase have been used as probes of the mechanism and sequence of assembly of the active complex. In the present study effects of mastoparans on activation of NADPH oxidase were investigated. Mastoparans are wasp venom cationic amphiphilic tetradecapeptides capable of modulation of various cellular activities. Natural mastoparans, as well as several synthetic mastoparan analogues, unrelated to oxidase components, blocked activation of the oxidase in the cell-free system (EC50 = 1.5 microM) and in guanosine 5′-[gamma-thio]triphosphate (GTP[S])/ATP-stimulated neutrophils permeabilized with streptolysin O. In the cell-free system the effect was not relieved by raising the detergent concentration and could not be ascribed to changes in critical micellar concentration values of the activating SDS or arachidonate. Chromatography of neutrophil cytosol on an immobilized mastoparan column suggested interaction of cytosolic p47-phox and p67-phox with the peptide. In spite of this interaction mastoparan did not interfere with translocation of p47-phox and p67-phox to the cell membranes.

Mastoparan (MP), a wasp venom peptide, is known both to interact with G-proteins and to alter membrane structure and function. To determine the structural requirements for these two aspects of MP action, we constructed several analogs of the peptide and characterized them using Swiss 3T3 cell membranes. The effects of these peptides were measured on: i) G-protein-mediated stimulation of phospholipase-C activity by GTPγS and bombesin and ii) the membrane enzyme activities, calcium-activated phospholipase-C and Na,K-ATPase. MP strongly inhibited all the above activities and caused membrane permeabilization. Substitution of one Lys residue by Gly at either the N- or C-terminal of the MP molecule resulted in peptides which selectively inhibited G-protein stimulated phospholipase-C with no or very slight membrane-perturbing effects. Introduction of additional Lys residues to MP led to the opposite effect. Thus, G-protein modulating and membrane disrupting actions of MP appear to be not necessarily linked, and may be separated.Copyright 1993, 1999 Academic Press