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Biomedical subjects

R M Roberts

Publications and source records attributed to R M Roberts.

288 records · Page 16Linked to original sources
PubMed1970

The incorporation of D-glucosamine-14C into root tissues of higher plants.

d-Glucosamine-1-(14)C was rapidly taken up from aqueous solution by both excised bean (Phaseolus vulgaris) and corn (Zea mays) root tips. The labeled glucosamine did not accumulate in the tissues, however, but was metabolized to N-acetyl-d-glucosamine, N-acetyl-d-glucosamine phosphates, and uridine diphosphate N-acetyl-d-glucosamine. Little or no label was detected in respiratory CO(2), glycolytic intermediates, or d-glucosamine 6-phosphate. Between 5 and 10% of the (14)C was recovered in high molecular weight ethanol-insoluble materials which could be solubilized readily with alkali or by treatment with proteases, and which yielded labeled glucosamine upon complete hydrolysis with HCl. Milder hydrolytic conditions released quantities of N-acetylglucosamine-(14)C plus labeled fragments of higher molecular weight. It is concluded that d-glucosamine-(14)C may be used to label specifically the amino sugar residues of plant as well as animal macromolecules. N-Acetyl-d-glucosamine acts similarly as a precursor, except that it is taken up at only about 1/10 the rate of glucosamine and hence is utilized less efficiently.

Glucosamine↗
PubMed1970

Studies on the pyrophosphorylases of wheat.

Adenosine diphosphoglucose and uridine diphosphoglucose pyrophosphorylase activities (class EC 2.7.7.9) were assayed radiochemically in ammonium sulfate fractions prepared from mature and germinating wheat grain. Both enzymes showed similar pH optima and metal ion requirements but differed markedly in their response to activation by d-glycerate 3-phosphate and inhibition by sulfate and phosphate.Their stability characteristics also differed greatly. While UDP-glucose pyrophosphorylase was very stable, ADP-glucose pyrophosphorylase rapidly lost activity in dilute solution and upon desalting on columns of Sephadex and was only partially stabilized when stored as a suspension in ammonium sulfate. Relatively high salt concentrations were required to maintain even short term stability. ADP-glucose and UDP-glucose pyrophosphorylases had apparent K(m) values for alpha-d-glucose 1-phosphate of 4.4 x 10(-5)m and 10(-3)m, respectively. In extracts from dry grain, the number of units of UDP-glucose pyrophosphorylase were about 30-fold greater than the number of units of ADP-glucose pyrophosphorylase. During germination, the activity of UDP-glucose pyrophosphorylase increased markedly in both the embryo and the endosperm, while ADP-glucose pyrophosphorylase fell slightly over the initial 4 days of germination.

Journal Article↗
PubMed1968

Inositol Metabolism in Plants. VI. Conversion of Myo-Inositol to Phytic Acid in Wolffiella floridana.

When Wolffiella floridana, an aquatic angiosperm in the family, Lemnaceae, was grown in axenic culture under continuous light in E medium containing 1.0% sucrose and a micromolar amount of (14)C-labeled myo-inositol (MI), MI was taken up by the growing plants and converted to phytic acid. After 13 weeks in labeled medium during which time there was a 1000-fold increase in fresh weight, 30% of the (14)C was recovered in ethanol insoluble residue. Extraction of this residue with EDTA released 70% of the label into solution. Phytic acid, identified by paper electrophoresis, ion exchange chromatography, and hydrolysis with phytase, accounted for most of this radioactivity although some label was also found in pentaphosphate and lower phosphate esters of MI. Very little MI was converted to cell wall polysaccharides under the conditions used. Results of this study indicate that Wolffiella floridana is a convenient tissue for the study of phytic acid biosynthesis under laboratory conditions.Lemna gibba G3, grown under short day conditions in medium of the same composition as that used for W. floridana, also formed labeled phytic acid as well as other labeled lower phosphate esters of MI.

Journal Article↗
PubMed1968

Inositol Metabolism in Plants. V. Conversion of Myo-inositol to Uronic Acid and Pentose Units of Acidic Polysaccharides in Root-tips of Zea mays.

The metabolism of myo-inositol-2-(14)C, d-glucuronate-1-(14)C, d-glucuronate-6-(14)C, and l-methionine-methyl-(14)C to cell wall polysaccharides was investigated in excised root-tips of 3 day old Zea mays seedlings. From myo-inositol, about one-half of incorporated label was recovered in ethanol insoluble residues. Of this label, about 90% was solubilized by treatment, first with a preparation of pectinase-EDTA, then with dilute hydrochloric acid. The only labeled constituents in these hydrolyzates were d-galacturonic acid, d-glucuronic acid, 4-O-methyl-d-glucuronic acid, d-xylose, and l-arabinose, or larger oligosaccharide fragments containing these units. Medium external to excised root-tips grown under sterile conditions in myo-inositol-2-(14)C contained labeled polysaccharide.When label was supplied in the form of d-glucuronate, the pattern of labeled uronic acid and pentose units in cell wall polysaccharides resembled that obtained from labeled myo-inositol, indicating that both substances were metabolized along a common path during polysaccharide formation, and that methylation occurred at a step subsequent to uronic acid formation. When label was supplied in the form of l-methionine-methyl-(14)C, 4-O-methyl-d-glucuronic acid was the only labeled monosaccharide component that survived enzymatic or acid hydrolysis.Zea mays endosperm, a known source of phytin, developed maximal phytase activity after the third day of germination. Results obtained here suggest that myo-inositol released by hydrolysis of phytin represents the initial precursor of a normal, possibly predominant pathway for the formation of uronic acids in plants.

Journal Article↗
PubMed1967

Incorporation of methanol into pectic substance.

Others have shown that l-methionine is utilized in the biosynthesis of methyl ester groups in pectic substance. Methanol, like l-methionine, is used for methyl ester biosynthesis by detached parsley leaves (Petroselinum crispum). When a combination of methanol-(3)H and methanol-(14)C is given to parsley leaves, methanol recovered from pectic substance by alkaline hydrolysis has a (3)H/(14)C ratio about one-fourth that of the mixture administered. Unlike l-methionine, methanol is oxidized prior to its utilization as a carbon source for methyl ester biosynthesis.Parsley leaves given methyl d-galacturonate-methyl-(14)C also form pectic substance in which methyl groups are labeled but incorporation appears to proceed by way of methanol metabolism after hydrolysis of methyl d-galacturonate.

Journal Article↗
PubMed1967

Inositol Metabolism in Plants. IV. Biosynthesis of Apiose in Lemna and Petroselinum.

The biosynthesis of apiose was investigated in cell wall polysaccharide of Lemna gibba G3 (duckweed) and in detached leaves of Petroselinum crispum (parsley). Lemna grown either in short days or in continuous light incorporated (14)C from a medium containing myo-inositol-2-(14)C into d-apiosyl and d-xylosyl units of cell wall polysaccharides. Labeled d-apiose was characterized by paper chromatography, by formation of labeled crystalline di-O-isopropylidene d-apiose, and by gas chromatography of trimethylsilyl derivatives of apiose and of its sodium borohydride reduction product, apiitol. Periodate oxidation of labeled apiose revealed 86 to 94% of the (14)C was located in formaldehyde fragments corresponding to C3' and C4. Comparison of this result with work reported by Grisebach and Doebereiner and by Beck and Kandler supports the conclusion that myo-inositol-2-(14)C was converted to d-apiose labeled specifically at C4.When l-arabinose-l-(14)C was supplied to Lemna, both l-arabinosyl and d-xylosyl units of cell wall polysaccharides became labeled, but no (14)C was found in d-apiose. Analysis of the medium external to the plants revealed the presence of a polysaccharide-like polymer that also contained labeled xylose and arabinose.Petroselinum leaves utilized myo-inositol-2-(3)H for the synthesis of apiose in apiin.These results provide direct evidence for a pathway of apiose biosynthesis involving d-glucuronic acid metabolism.

Journal Article↗
PubMed1966

Inositol Metabolism in Plants. III. Conversion of Myo-inositol-2-H to Cell Wall Polysaccharides in Sycamore (Acer pseudoplatanus L.) Cell Culture.

Prolonged growth of cell cultures of sycamore (Acer pseudoplatanus L.) on agar medium containing myo-inositol-2-(3)H resulted in incorporation of label predominately into uronosyl and pentosyl units of cell wall polysaccharides. Procedures normally used to distinguish between pectic substance and hemicellulose yielded carbohydrate-rich fractions with solubility characteristics ranging from pectic substance to hemicellulose yet the uronic acid and pentose composition of these fractions was decidedly pectic. Galacturonic acid was the only uronic acid present in each fraction. Subfractionation of alkali-soluble (hemicellulosic) polysaccharide by neutralization followed by ethanol precipitation gave 3 fractions, a water-insoluble, an ethanol-insoluble, and an ethanol-soluble fraction, each progressively poorer in galacturonic acid units and progressively richer in arabinose units; all relatively poor in xylose units.Apparently, processes involved in biosynthesis of primary cell wall continued to produce pectic substance during cell enlargement while processes leading to biosynthesis of typically secondary cell wall polysaccharide such as 4-0-methyl glucuronoxylan were not activated.

Journal Article↗
PubMedDate not supplied

Possible function of carbohydrate on glycoproteins secreted by the pig uterus during pregnancy.

Uteroferrin is a purple iron-containing acid phosphatase secreted by the porcine uterus under the influence of the hormone, progesterone. It is synthesized by the glandular epithelial cells of the uterine endometrium and during pregnancy is taken up by specialized structures (areolae) opposite each uterine gland. Uteroferrin is then released into the fetal circulation and cleared by the liver or fetal kidney. A major role in iron transport to the fetus has been proposed. Uteroferrin, as purified from uterine secretions of pigs, possesses mainly high mannose (predominantly Man5 and Man6) chains. These oligosaccharide chains of uteroferrin appear to be responsible for its binding and uptake by reticuloendothelial cells of the fetal liver which is the major site of erythropoiesis of the fetus. Uteroferrin, although implicated in transplantal iron transport, also possesses many of the properties of a lysosomal enzyme and, when newly synthesized, carries the so-called lysosomal recognition marker, mannose 6-phosphate. The phosphate group is masked by a covering N-acetylglucosamine residue, a feature which may account for its secretion rather than retention within lysosomes. Evidence is also presented that the oligosaccharide chains of newly synthesized uteroferrin are larger than those of the mature form and are trimmed after secretion. The phosphate group is also removed. It is not clear whether uteroferrin carbohydrate is implicated in the movement of the glycoprotein across the placenta as well as its uptake by the fetal liver.

Acid Phosphatase↗
PubMedDate not supplied

Interferon-like sequence of ovine trophoblast protein secreted by embryonic trophectoderm.

In most species the length of a pregnancy exceeds that of the luteal phase of the ovarian cycle. The conceptus within the uterus, therefore, is believed to produce a substance or substances which directly or indirectly prolong the lifespan of the corpus luteum and prevent a return to ovarian cyclicity. This phenomenon is known as maternal recognition of pregnancy. The active substance implicated in signalling maternal recognition of pregnancy in the sheep is an embryonic secretory protein, known as ovine trophoblast protein-1 (oTP-1) (refs 2-4), which is targeted in a paracrine manner to the uterine epithelium of the mother. We report here the primary amino-acid sequence of oTP-1 as inferred from a cloned complementary DNA and demonstrate that the protein is most probably an interferon-alpha.

Amino Acid Sequence↗