Monosaccharide composition analysis of oligosaccharides and glycoproteins by high-performance liquid chromatography

A simple and sensitive high-performance liquid chromatography (HPLC)-based method for complete monosaccharide composition analysis of oligosaccharides and glycoproteins is described. In this method, an oligosaccharide or glycoprotein is first hydrolyzed using an optimized method to give the constituent monosaccharides, which are subsequently labeled with 1-phenyl-3-methyl-5-pyrazolone (PMP) as previously described by Honda et al. (Anal, Biochem. 180, 351-357, (1989)). The labeled monosaccharides are separated by reverse-phase HPLC using a column developed especially for this purpose, monitored by uv absorbance at 245 nm, and quantitated by their integration values relative to standards. Sialic acids are acid-labile keto-sugars. They are, therefore, released with neuraminidases or by mild acid hydrolysis and then converted with neuraminic acid aldolase to their corresponding mannosamine derivatives, which are then PMP-labeled, separated, and quantitated as described above. Individual sialic acids including N-acetyl and N-glycolyl neuraminic acids are well resolved and quantitated by this method. This method has proven to be highly sensitive, requiring only 1 pmol for reliable detection. Quantitative analysis of neutral and amino sugars from both oligosaccharide and glycoprotein samples can be achieved using one acid hydrolysis and a set of equal molar monosaccharide standards. Similarly, quantitation of sialic acids works equally well with both free oligosaccharide and glycoprotein samples. Monosaccharide compositions of oligosaccharides and glycoproteins determined by this method were found to be highly accurate.

Mapping the binding-site crevice of the dopamine D2 receptor by the substituted-cysteine accessibility method

The binding site of the dopamine D2 receptor, like that of other homologous G protein-coupled receptors, is contained within a water-accessible crevice formed among its seven membrane-spanning segments. We have developed a method to map systematically all the residues forming the surface of this binding-site crevice, and we have applied this method to the third membrane-spanning segment (M3). We mutated, one at a time, 23 residues in and flanking M3 to cysteine and expressed the mutant receptors heterologously. Ten of these mutants reacted with charged, hydrophilic, lipophobic, sulfhydryl-specific reagents, added extracellularly, and were protected from reaction by a reversible dopamine antagonist. Thus, the side chains of these residues are exposed in the binding-site crevice, which like M3 extends from the extracellular to the intracellular side of the membrane. The pattern of exposure is consistent with a short loop followed by six turns of an alpha helix.

Sequence, mapping and disruption of CCC2, a gene that cross-complements the Ca(2+)-sensitive phenotype of csg1 mutants and encodes a P-type ATPase belonging to the Cu(2+)-ATPase subfamily

We have isolated, sequenced, mapped and disrupted a gene, CCC2, from Saccharomyces cerevisiae. This gene displays non-allelic complementation of the Ca(2+)-sensitive phenotype conferred by the csg1 mutation. Analysis of the CCC2p amino acid sequence reveals that it encodes a member of the P-type ATPase family and is most similar to a subfamily thought to consist of Cu2+ transporters, including the human genes that mutate to cause Wilson disease and Menkes disease. The ability of this gene, in two or more copies, to reverse the csg1 defect suggests that Ca(2+)-induced death of csg1 mutant cells is related to Cu2+ metabolism. Cells without CCC2 require increased Cu2+ concentrations for growth. Therefore CCC2p may function to provide Cu2+ to a cellular compartment rather than in removal of excess Cu2+.

Modulation of lipid metabolism at rat hepatic subcellular sites by female sex hormones

The present studies examine the modulation of lipoprotein metabolism at subcellular sites in the liver by female sex hormones. Subcutaneous injection of ethinyl estradiol (5 mg/kg) decreased both triacylglycerol (TG) lipase activity and neutral cholesteryl ester (CE) hydrolase activity in hepatic endosomes while increasing lysosomal lipid hydrolysis. These data suggest that estrogen may induce a shift in the site of intracellular lipid catabolism similar to that found in fasting animals [1]. This work also shows that TG-lipase activity is increased in the CURL and MVB endosomal fractions of ovariectomized rats compared to that found in the equivalent endosomal compartments of age-matched intact female controls. These observations are consistent with an inhibition of endosomal lipase by female sex hormones under physiologic conditions.

A detailed structural characterization of ribonuclease B oligosaccharides by 1H NMR spectroscopy and mass spectrometry

The structures of ribonuclease B oligosaccharides have previously been shown to be high mannose type by methylation analyses and sequential exoglycosidase digestion. Due to the unique nature of these oligosaccharides, in that all mannosyl residues are attached by alpha-(1-->2)-linkages beyond the branch points, methylation analysis fails to solve the exact structures beyond Man5. Therefore, we have undertaken this study using 1H nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. In this study, bovine pancreatic ribonuclease B was first reduced and carboxymethylated, and was then deglycosylated by peptide/N-glycosidase F (PNGase F). The released oligosaccharides were fractionated by Bio-Gel P-4 chromatography to give five pools, Man5 through Man9. The structures of the oligosaccharide pools were then studied by laser desorption time of flight mass spectrometry and 1H NMR spectroscopy at 300 MHz. For Man5, Man-A and Man-B are attached in alpha-(1-->3)- and alpha-(1-->6)-linkages to the alpha-(1-->6)-linked Man-4' of the pentasaccharide core structure. For Man6, Man-C is linked alpha-(1-->2) to the alpha-(1-->3)-linked Man-4. Man7 exists as three structural isomers, and has the additional mannosyl residue (Man-D) linked alpha-(1-->2) to Man-A, Man-B, and Man-C is linked alpha-(1-->2) to the alpha-(1-->3)-linked Man-4. Man-7 exists as three structural isomers, with the additional two mannosyl residues linked alpha-(1-->2) to Man-A, Man-B, and Man-C. For each position, Man-A, Man-B, and Man-C, the extent of occupancy by one of the additional alpha-(-->)-linked mannosyl residues was 15, 94, and 91%, respectively. Man9 is a single component, with the three additional mannosyl residues linked alpha-(1-->2) to Man-A, Man-B, and Man-C, respectively. The relative molar proportions of Man5 to Man9 are 57, 31, 4, 7, and 1%, respectively. This report presents for the first time the complete structural characterization of the oligosaccharides from ribonuclease B.

Sequence, mapping and disruption of CCC1, a gene that cross-complements the Ca(2+)-sensitive phenotype of csg1 mutants

We have isolated, sequenced, mapped and disrupted a novel gene, CCC1, from Saccharomyces cerevisiae. This gene displays non-allelic complementation of the Ca(2+)-sensitive phenotype conferred by the csg1 mutation. The ability of this gene, in two copies per cell, to reverse the csg1 defect suggests it may have a role in regulating Ca2+ homeostasis. The sequence of CCC1 indicates that it encodes a 322 amino acid, membrane-associated protein. The CCC1 gene is located on the right arm of chromosome XII.

N-glycosylation site mapping of human serotransferrin by serial lectin affinity chromatography, fast atom bombardment-mass spectrometry, and 1H nuclear magnetic resonance spectroscopy

This report describes the N-glycosylation site mapping of human serotransferrin (h-STF). Reduced and S-carboxymethylated h-STF was digested with trypsin or chymotrypsin. Glycopeptides in the proteolytic digests were isolated by serial concanavalin A (Con A), Sambucus nigra agglutinin (SNA), and Phaseolus vulgaris leukoagglutinin (LPHA) affinity chromatography and subjected to preliminary analysis by 1H NMR spectroscopy. The glycopeptide fractions were then individually digested with N-glycanase. One part of the digest of each fraction was analyzed by fast atom bombardment-mass spectrometry (FAB-MS) to identify the peptide sequences of the glycosylation sites. The other part was used to isolate the oligosaccharide by the corresponding lectin affinity chromatography and to characterize the structures of the isolated oligosaccharides by 1H NMR spectroscopy and FAB-MS. The oligosaccharides in the Con A-bound fraction were shown to have bi-alpha(2-->6)-sialyl, diantennary structures. The SNA-bound fraction was shown to contain trisialyl, triantennary structures. Di- and triantennary oligosaccharides were found to occur on each of the two N-glycosylation sites of h-STF (Asn413 and Asn611) in the ratio of approximately 85:15. The SNA-bound glycopeptides were further fractionated by LPHA affinity chromatography. Two different oligosaccharides were characterized, namely, a trisialyl 2,4-triantennary and a trisialyl 2,6-triantennary glycan. The ratio of 2,4-triantennary vs 2,6-triantennary oligosaccharides attached to glycosylation site Asn413 was found to be approximately 5:1, whereas the two isomeric triantennary oligosaccharides were found to be attached to glycosylation site Asn611 in the ratio approximately 1:1.

Alterations in lipolytic activity at hepatic subcellular sites of fed and fasted rats

This study investigates the relationship between the nutritional state of rats and lipid metabolism in distinct hepatic intracellular sites. Hepatic uptake of both protein and triacylglycerol (TG) moieties of injected very low-density lipoprotein (VLDL) is increased in fasted rats compared with fed controls. The VLDL-TG hydrolysis rate is increased in the plasma of fasted rats. This is shown by a higher ratio of labeled free fatty acid (FFA) to TG (FFA/TG). In both fed and fasted rats, a much greater increase of the labeled FFA/TG ratio in endosomes, compared with that in plasma, shows that further TG hydrolysis occurs in prelysosomal compartments. However, in fasted rats, this increase (18-fold) is much less than that in fed rats (69-fold). This observation is supported by the finding of significantly lower TG-lipase activity at pH 5, 7, and 8.6 in the endosomes of fasted rats. In contrast, during fasting, TG-lipase activity in whole liver homogenate and in isolated lysosomes is increased at pH 5. These observations suggest that after feeding there is a shift in intracellular lipolytic activity from lysosomes to prelysosomal organelles.

Essential histidine residues in dextransucrase: chemical modification by diethyl pyrocarbonate and dye photo-oxidation

Treatment of Leuconostoc mesenteroides B-512F dextransucrase with diethyl pyrocarbonate (DEP) at pH 6.0 and 25 degrees or photo-oxidation in the presence of Rose Bengal or Methylene Blue at pH 6.0 and 25 degrees, caused a rapid decrease of enzyme activity. Both types of inactivation followed pseudo-first-order kinetics. Enzyme partially inactivated by DEP could be completely reactivated by treatment with 100 mM hydroxylamine at pH 7 and 4 degrees. The presence of dextran partially protected the enzyme from inactivation. At pH 7 or below, DEP is relatively specific for the modification of histidine. DEP-modified enzyme showed an increased absorbance at 240 nm, indicating the presence of (ethoxyformyl)ated histidine residues. DEP modification of the sulfhydryl group of cysteine and of the phenolic group of tyrosine was ruled out by showing that native and DEP-modified enzyme had the same number of sulfhydryl and phenolic groups. DEP modification of the epsilon-amino group of lysine was ruled out by reaction at pH 6 and reactivation with hydroxylamine, which has no effect on DEP-modified epsilon-amino groups. The photo-oxidized enzyme showed a characteristic increase in absorbance at 250 nm, also indicating that histidine had been oxidized, and no decrease in the absorbance at 280 nm, indicating that tyrosine and tryptophan were not oxidized. A statistical, kinetic analysis of the data on inactivation by DEP showed that two histidine residues are essential for the enzyme activity. Previously, it was proposed that two nucleophiles at the active site attack bound sucrose, to give two covalent D-glucosyl-enzyme intermediates. We now propose that in addition, two imidazolium groups of histidine at the active site donate protons to the leaving, D-fructosyl moieties. The resulting imidazole groups then facilitate the formation of the alpha-(1----6)-glycosidic linkage by abstracting protons from the C-6-OH groups, and become reprotonated for the next series of reactions.

Factors affecting the stability and separation of biogenic amines and their metabolites. Simultaneous measurement by HPLC with electrochemical detection

We describe a simple and sensitive method for the rapid and simultaneous quantification of dopamine, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, serotonin, 5-hydroxyindoleacetic acid, and 5-hydroxytryptophan in the picogram range in small samples of brain tissue. After minimal sample preparation the amines were analyzed utilizing isocratic separation and reversed-phase high-performance liquid chromatography with amperometric detection. The effects of pH and methanol concentration in the solvent on the retention times of the amines on two different C-18 columns were investigated. Stabilities of the amines in solution were determined under various conditions. Light and air were found to be detrimental to the stability of indoles. In the absence of light, their stability was dependent on temperature and the presence of air; however, in the absence of air, light and/or temperature had little effect. The catechols were stable under most of these conditions. The assay has been applied to study the postmortem stability of dopamine, serotonin, and their metabolites in the striatum of rat brain. In the striatum 4 hr after death, the content of dopamine and 3,4-dihydroxyphenylacetic acid decreased by less than 20%, and 3-methoxytyramine increased by 158%, with no changes in serotonin, 5-hydroxyindoleacetic acid, and homovanillic acid.

Synthesis and biological activity of highly potent octapeptide analogs of somatostatin

In the search for selective and long-acting analogs of somatostatin, nearly 200 compounds were synthesized by solid-phase methods, purified, and tested biologically. Among these octapeptides, some contained N-terminal (Formula: see text) were 177 times and 113 times more potent, respectively, than somatostatin in tests for inhibition of growth hormone release. These two octapeptides containing tyrosine and valine in positions 3 and 6, respectively, were more active and more selective than their Phe-3 and Thr-6 counterparts, D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-NH2 and D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Trp-NH2. D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 was also about 6 times more potent than its L-Trp-4 diastereoisomer. The analogs D-Phe-Cys-Tyr-Lys-Val-Cys-Thr-NH2 and D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2 showed a prolonged duration of action and were able to inhibit growth hormone release for at least 3 hr. Analogs of both Phe-3/Thr-6 and Tyr-3/Val-6 classes also suppressed the release of insulin and glucagon in rats and pentagastrin-induced secretion of gastric acid in dogs, but their potencies in these tests were much smaller than the growth-hormone-release inhibitory activity. Some of these analogs possessed antitumor activities as shown by the inhibition of growth of animal models of prostate, mammary, and ductal pancreatic tumors.