References: Lecithin
Biopolymers. 1992 Dec;32(12):1765-73.
Interaction of substance P and its N- and C-terminal fragments with Ca2+: implications for hormone action.
Ananthanarayanan VS, Orlicky S.
Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada.
In an attempt to understand the role of Ca2+ on the bioactive conformation of peptide hormones, we have examined the interaction between Ca2+ and the neuropeptide substance P. Using CD spectroscopy to monitor conformational changes caused by Ca2+ binding, we found no significant binding of the cation by substance P in water. However, a substantial conformational change occurred in the hormone on Ca2+ addition in trifluoroethanol or an 80:20 (v/v) mixture of acetonitrile and trifluoroethanol. A biphasic binding of Ca2+ was observed in these solvents with saturation at 2 cations per hormone molecule. Mg2+ caused a relatively smaller conformational change in the hormone. A peptide corresponding to residues 1-7 at the N-terminal fragment of substance P showed a weak nonsaturating binding of Ca2+ in the nonpolar solvents whereas the 7-11 C-terminal fragment peptide displayed a binding indicative of an 1:1 Ca2+/peptide complex. Ca2+ binding by the hormone and the 7-11 fragment was also monitored by changes in fluorescence of the phenylalanyl residues. The results support the conclusion drawn from the CD data about a distinct Ca2+ binding site in the C-terminal part of substance P. The Kd values obtained from fluorescence data were 160 microM for Ca2+ and 1 mM for Mg2+ binding by substance P. The hormone and the two peptide fragments were also tested for their effect on the stability of dimyristoyl lecithin vesicles. Substance P and the N-terminal fragment caused no significant leakage of either fluorescent dyes or K+ trapped in the vesicles. Nor did they cause membrane fusion as monitored by the fluorescence quenching method.(ABSTRACT TRUNCATED AT 250 WORDS)
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1282041&dopt=Abstract lecithin
Sheng Li Xue Bao. 1992 Dec;44(6):533-40.
[Channel-forming activity at planar lipid bilayer of the membrane active polypeptide B form venom of Bungarus fasciatus]
[Article in Chinese]
Shi YL, Wang WP, Zhang H, Xu K.
Shanghai Institute of physiology, Academia Sinica.
Using planar lipid bilayer formed by lecithin and cholesterol (20 and 5 mg/ml respectively in N-decane) the channel-forming activity of the membrane active polypeptide B(BMAP B) from the venom of Bungarus fasciatus was investigated. Under the existence of a voltage or a salt concentration gradient between two sides of the bilayer, unit conductance fluctuation and a decrease in steady state resistance accompanying BMAP B incorporation and channel formation were observed. By measuring the reversal potential in an asymmetric solution, the selectivity of the BMAP B-channel was estimated having a value of PK/PC1 = 1.4. Divalent cations, such as Ba2+, Ca2+ inhibited the channel activity as they did in biomembranes. These data might provide an explanation for the depolarizing effect of the membrane active polypeptide on the native membranes.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1284572&dopt=Abstract lecithin
J Neurosci. 1988 Aug;8(8):2961-6.
The adhesion molecule on glia (AMOG) incorporated into lipid vesicles binds to subpopulations of neurons.
Antonicek H, Schachner M.
Department of Neurobiology, University of Heidelberg, FRG.
To investigate the functional role of the novel adhesion molecule on glia (AMOG) in cell surface interactions, immunoaffinity-purified AMOG was incorporated into liposomes and measured for its ability to bind to cells in monolayer cultures. AMOG could be incorporated into liposomes in functionally active form after solubilization from membranes in 1% cholate buffer containing soybean lecithin, elution from the AMOG monoclonal antibody column with 4 M MgCl2, containing 1% octylglucoside, and removal of detergent for liposome incorporation by gel filtration. AMOG-containing liposomes bound to neurons, but not to oligodendrocytes, astrocytes, or fibroblasts in early postnatal cerebellar cultures. AMOG-containing liposomes also bound to the pheochromocytoma cell line PC12, but not to neurons in cultures of spinal cord and dorsal root ganglia after various times in vitro. Fab fragments of monoclonal AMOG antibodies, but not of L3 monoclonal antibodies directed against a carbohydrate structure on AMOG, inhibited binding of liposomes. Liposome binding was not reduced by preincubation of cerebellar cells with antibodies to AMOG, to the neuron adhesion molecule L1, the neural cell adhesion molecule N-CAM, or the L3 carbohydrate structure, nor with 2 monoclonal antibodies reacting with neuronal cell surface glycoproteins related to the L2/HNK-1 family. These results show that AMOG is indeed a ligand in adhesion and binds to particular subpopulations of neurons in L1- and N-CAM-independent mechanisms.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2457661&dopt=Abstract lecithin
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