Binding of simple carbohydrates and some N-acetyllactosamine-containing oligosaccharides to Erythrina cristagalli agglutinin as followed with a fluorescent indicator ligand

Erythrina cristagalli agglutinin, a dimeric lectin [J. L. Iglesias, et al. (1982) Eur. J. Biochem.123, 247–252] was shown by equilibrium dialysis to be bivalent for 4-methylumbelliferyl-β-d-galactoside. Upon binding to the lectin, this ligand showed a difference absorption spectrum with two maxima (at 322 and 336 nm) of equal intensity (Δ? = 1.2 × 10³m^?1 cm^?1). A similar spectrum with a comparable value of Δ? was obtained with 4-methylumbelliferyl-N-acetyl-β-d-galactosaminide. Binding of methyl-α-d-galactoside, lactose, and N-acetyllactosamine all produced small but equally intense protein difference spectra with a maximum (Δ? = 2.8 × 10² M^?1 cm^?1) at 291.6 nm. Upon binding of N-dansyl-d-galactosamine to the lectin, there was a fivefold increase in fluorescence intensity of this ligand. The association constant for N-dansyl-d-galactosamine was caused by a very favorable ΔS° of the dansyl group without affecting the strictly carbohydrate-specific character of binding. N-Dansyl-d-galactosamine was employed as a fluorescent indicator ligand in substitution titrations. This involved the use of simple carbohydrates, N-acetyllactosamine, and oligosaccharides which occur in the carbohydrate units of N-glycoproteins; the latter were Gal(β → 4)GlcNAc(β1 → 2)Man, Gal(β1 → 4)GlcNAc(β1 → 6)Man, and Gal(β1 → 4)GlcNAc(β1 → 6)[Gal(β1 → 4)GlcNAc(β1 → 2)]Man. The titrations were performed at two temperatures to determine the thermodynamic parameters. In the series N-acetyl-d-galactosamine, methyl-α-d-galactoside, and lactose, ?ΔH° increased from 24 to 41 kJ mol^?1; it increased further for N-acetyllactosamine and then remained unchanged for the N-acetyllactosamine-containing oligosaccharides (55 ± 1 kJ mol^?1). This indicated that the site specifically accommodated the disaccharide structure with an important contribution of the 2-acetamido group in the penultimate sugar. Beyond this, no additional contacts seemed to be formed. This conclusion also followed from considerations of ΔS° values which became more unfavorable in the above series (?23 to ?101 ± 4 J mol^?1 K^?1); the most negative value of ΔS° was observed with N-acetyllactosamine and the three N-acetyllactosamine-containing oligosaccharides.     

The antagonism of bombesin in the CNS by substance P analogues

The ability of substance P analogues to inhibit the action of bombesin in the CNS was investigated using receptor binding and biological assays. The putative substance P antagonists inhibited binding to central receptors for both substance P and bombesin-like peptides. Spantide, which was the most potent analogue tested, reversed the bombesin induced hypothermia and grooming. Therefore the putative substance P antagonists may also antagonize the actions of bombesin in the CNS     

Bombesin-like peptides in small cell lung cancer: biochemical characterization and secretion from a cell line

High intracellular levels of BN-like peptides are present in tumors and cell lines of small cell carcinoma of the lung (SCCL) as well as the putative precursor cells of this tumor, the pulmonary endocrine cell. In cell line NCI-H209 the density of bombesin-like peptides was 8.9 +/- 1.1 pmol/mg total protein. Gel filtration chromatography of an extract of these cells revealed one major peak of immunoreactivity which coeluted with synthetic bombesin (1620 daltons). Also, high pressure liquid chromatography revealed one major peak of immunoreactivity was present which eluted before synthetic peptide. Therefore, SCCL bombesin-like peptides may be of similar size but are more hydrophilic than synthetic peptide. Cells maintained in culture continuously release bombesin-like peptides into the growth medium. Also, high concentrations of K+ stimulated the secretion of immunoreactive bombesin from cell lines in a Ca++-dependent manner. These SCCL bombesin-like peptides may function as important regulatory agents in the malignant lung.     

An ionophoretic model for the study of calcium-calcium exchange

A Pressman cell was used to study the Br-X537A-mediated translocation of ⁴⁵Ca from one aqueous phase into another across an immiscible organic phase. In this system, an increase in the concentration of ⁴⁰Ca in one chamber (mimicking the extracellular compartment) resulted in an increased efflux of ⁴⁵Ca added in trace amount to the other chamber (simulating the cytosolic compartment). Such a Ca-Ca exchange process was also observed when the concentration of ionophore was increased, and could be blocked by the organic Ca-antagonist suloctidil. However, no Ca-Ca exchange occurred when the downhill rate of ⁴⁰Ca translocation was increased by use of a pH gradient. This ionophoretic model also suggests that a low intracellular concentration of Ca tends to maintain Ca influx at a low rate, and that the asymetrical distribution of Ca facilitates rather than impeeds the ionophoretic extrusion of intracellular Ca against its chemical gradient.