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Biomedical subjects

R H Hamilton

Publications and source records attributed to R H Hamilton.

At least 37 records · Page 2Linked to original sources
PubMed1980

Comparative metabolism of 2,4-dichlorophenoxyacetic Acid in cotyledon and leaf callus from two varieties of soybean.

Only quantitative differences were observed in the metabolism of [1-(14)C]2,4-dichlorophenoxyacetic acid (2,4-D) by soybean cotyledon callus as influenced by variety (Acme and Amsoy), source of tissue (cotyledon, leaf and root) and age. All tissues metabolized 2,4-D to water-soluble (glycosides) and ether-soluble (primarily amino acid conjugates) metabolites.In young (3- to 4-week-old) Amsoy cotyledon or leaf callus tissue the free 2,4-D increased proportionately with the external 2,4-D concentration while in older (6- to 8-week-old) tissue the amino acid conjugates increased in this manner. Thus, in the older Amsoy tissue apparent regulation of the internal 2,4-D level (1.5-3.5 nmoles per gram fresh weight) was observed. In 3- or 6-week-old Acme cotyledon callus 2,4-D accumulated with an increase in the external 2,4-D concentration with no evidence for regulation of internal 2,4-D levels.

Journal Article↗
PubMed1980

Metabolism of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Soybean Root Callus : EVIDENCE FOR THE CONVERSION OF 2,4-D AMINO ACID CONJUGATES TO FREE 2,4-D.

An auxin-requiring soybean root callus metabolized [1-(14)C]-2,4-dichlorophenoxyacetic acid (2,4-D) to diethyl ether-soluble amino acid conjugates and water-soluble metabolites. The uptake in tissue varied with incubation time, concentration, and amount of tissue. Uptake was essentially complete (80%) after a 24-hour incubation and the percentage of free 2,4-D in the tissue fell to its lowest point at this time. At later times, the percentage of free 2,4-D increased and the percentage of amino acid conjugates decreased, whereas the percentage of water-soluble metabolites increased only slightly. Similar trends were seen if the tissue was incubated for 24 hours in radioactive 2,4-D, followed by incubation in media without 2,4-D for 24 hours. Inclusion of nonlabeled 2,4-D during the 24-hour chase period did not reduce amino acid conjugate disappearance but did reduce the percentage of free [1-(14)C]2,4-D. Thus, an external supply of 2,4-D does not directly prevent amino acid conjugate metabolism in this tissue. It is concluded that 2,4-D amino acid conjugates were actively metabolized by this tissue to free 2,4-D and water-soluble metabolites.

Journal Article↗
PubMed1979

Paraneoplastic vasculitis of nerve: a remote effect of cancer.

The development of mononeuritis multiplex brought three men to medical attention weeks to months prior to the diagnosis of a malignancy. In each case, sural nerve biopsy exhibited active wallerian degeneration with vasculitis. Two of the men died and at autopsy were found to have clinically unrecognized oat cell carcinoma and carcinomatous sensory neuropathy with brainstem encephalitis. The third patient is still alive but was found to have a lymphoma and has subsequently developed a liposarcoma. The vasculitis in all 3 cases seems limited mainly to the peripheral nervous system. Mononeuritis multiplex due to vasculitis may represent a new remote effect of cancer on the nervous system.

Brain Stem↗
PubMed1979

Purification and characterization of agrocin 84.

A procedure for the rapid purification of milligram quantities of agrocin 84, a bacteriocin-like compound produced by Agrobacterium radiobacter strain K-84, has been developed. This procedure, which employs charcoal adsorption, ion-exchange, sieving chromatography, and continuous-flow electrophoresis, can yield agrocin 84 which is 65% pure on a dry weight basis. The purest preparations were strongly ultraviolet absorbing, with a maximum at 264 nm (epsilon 7.0/264 = 22,675 cm2 - M-1) and a minimum at 227 nm (ratio of 264 to 227 nm, 6.00). As has been reported, agrocin 84 contains an unusual phosphoramidate or 6-N-acyl linkage to adenine. Adenine, glucose, and phosphate are present in a 1:1:2 molar ratio. The molecular weight was estimated to be 1,350.

Adenine Nucleotides↗
PubMed1978

Metabolism of 2,4-dichlorophenoxyacetic Acid in soybean root callus and differentiated soybean root cultures as a function of concentration and tissue age.

The metabolism of [1-(14)C]2,4-dichlorophenoxyacetic acid (2,4-D) in soybean (Glycine max [L.] Merrill var. Amsoy) root callus and in differentiated soybean root cultures was investigated as a function of pesticide concentration and age of tissue. The chronological age of the tissue was found to be correlated with the mitotic index which reached a peak at 2 weeks and then declined. The metabolism of 2,4-D changed with age of the root callus tissue. The amount of free 2,4-D found in 3-week-old root callus tissue rapidly increased as the concentration of 2,4-D in the medium was increased from 10(-6) to 10(-5) molar, whereas the low level of aqueous (glycosides) and ether soluble metabolites (2,4-D amino acid conjugates) increased slowly. With 9-week-old root callus tissue, the amount of free 2,4-D remained at a relatively low, constant level (saturation level) as the concentration of 2,4-D in the medium increased. Under these conditions the aqueous metabolites increased only slightly but the ether fraction (2,4-D amino acid conjugates) rapidly increased. Thus, the older root callus tissue appeared to regulate the level of free 2,4-D at about 4 nanomoles per gram by converting any excess 2,4-D into amino acid conjugates.In 3-week-old, differentiated root cultures the metabolism of 2,4-D closely paralleled the metabolism found in the older 9-week-old callus tissue. The saturation level of free 2,4-D found in this tissue was only about 1 to 2 nanomoles per gram.

Journal Article↗
PubMed1977

Metabolism of Indole-3-acetic Acid: IV. Biological Properties of Amino Acid Conjugates.

The biological activity of 20 l-alpha-amino acid conjugates of indole-3-acetic acid (IAA) to stimulate cell elongation of Avena sativa coleoptile sections and to stimulate growth of soybean cotyledon tissue cultures has been examined at concentrations of 10(-4) to 10(-7)m. In the Avena coleoptile test, most of the amino acid conjugates stimulated elongation. Several of the conjugates stimulated as much elongation as IAA but their half-maximum concentrations tended to be higher. Some of the more active conjugates were alanine, glycine, lysine, serine, aspartic acid, cystine, cysteine, methionine, and glutamic acid.In the soybean cotyledon tissue culture test, all of the l-alpha-amino acid conjugates of IAA stimulated growth except for the phenylalanine, histidine, and arginine conjugates. Most of the conjugates produced responses at least as great as that caused by IAA. Conjugates with half-maximum concentrations lower than IAA included cysteine, cystine, methionine, and alanine. These conjugates exceed the IAA-induced callus growth at all tested concentrations. Other conjugates significantly better than IAA at 10(-6)m were serine, glycine, leucine, proline, and threonine.

Journal Article↗
PubMed1977

Hypoliquorreic headache and pneumocephalus caused by thoraco-subarachnoid fistula.

One month after having a right upper lobectomy to remove a squamous cell carcinoma, a 43-year-old man presented with a 4-day history of postural headache, worsened by standing and relieved by lying. Skull films showed prominent ventricular pneumocephalus. Iophendylate myelography was unrewarding, but isotope cisternography revealed a CSF fistula at the T4 level, extending into the thoracic cavity. Thoracoplastic removal of the first four ribs successfully prevented air passage and the patient had a rapid uneventful recovery.

Adult↗
PubMed1976

Indoleacetic Acid synthesis in soybean cotyledon callus tissue.

Growth of an auxin-requiring soybean cotyledon callus tissue (Glycine max L., Merr. var. Acme) was promoted by tryptophan, tryptamine, indole, indoleacetamide and, to a very slight degree, anthranilic acid. When tryptophan-3-(14)C was supplied in the growth medium, labeled indoleacetic acid (IAA) was found in both the tissue and the medium. Medium, from which the cells had been removed, was also found to convert labeled tryptophan to IAA. Soybean callus contained 0.044 mumole/g free tryptophan, but this is apparently not available for conversion to IAA. These results suggest that while exogenously supplied trytophan could elevate a specific internal pool where IAA synthesis occurs some of the growth on a tryptophan medium can be accounted for by external conversion.

Journal Article↗
PubMed1976

Metabolism of Indole-3-Acetic Acid: II. Oxindole Pathway in Parthenocissus tricuspidata Crown-Gall Tissue Cultures.

An indoleacetic acid oxidase preparation from an acetone powder of Parthenocissus tricuspidata crown-gall tissue has been examined. An intermediate in the reaction is 3-hydroxymethyloxindole and nonenzymic conversion of it to 3-methyleneoxindole was observed. Neither reaction mixtures nor 3-methyleneoxindole have any auxin-like activity in Avena or wheat coleoptile bioassays. In vivo studies show that although 53% decarboxylation of indoleacetic acid was observed in 48 hours, only a small amount of 3-methyloxindole could be recovered from the medium. The other decarboxylated products remain to be identified but are not 3-hydroxymethyloxindole or 3-methyleneoxindole.

Journal Article↗
PubMed1976

Metabolism of Indole-3-Acetic Acid: III. Identification of Metabolites Isolated from Crown Gall Callus Tissue.

The metabolism of labeled indole-3-acetic acid (IAA-2-(14)C) was investigated in Parthenocissus tricuspidata crown gall callus tissue. After 48 hours incubation, 85 to 90% of the supplied IAA was taken up by the tissue, and of that taken up, about 45% was conjugated with five amino acids. The conjugates found were aspartic and glutamic acid (minor ones) as well as glycine, alanine, and valine (major ones). The last four are being reported for the first time as metabolites of IAA. These conjugates were identified through their chromatographic properties, hydrolysis products, and their mass spectra. The possible significance of these amino acid conjugates is discussed.

Journal Article↗
PubMed1972

The relative amounts and identification of some 2,4-dichlorophenoxyacetic Acid metabolites isolated from soybean cotyledon callus cultures.

Soybean (Glycine max L.) cotyledon callus grown on radioactive 2,4-dichlorophenoxyacetic acid (2,4-D-1-(14)C) as an auxin produced 2,4-D metabolites, which qualitatively and quantitatively changed with time. Water soluble fractions from the tissue exhibited a steady increase in radioactivity during the course of 24 days. Following beta-glucosidase treatment, at least eight aglycones were obtained from the water soluble fraction of the tissue after 8 days. The metabolite, 4-hydroxy-2,5-dichlorophenoxyacetic acid was the most abundant aglycone during the entire 32 day growth period while 4-hydroxy-2,3-dichlorophenoxyacetic acid was detected as a minor metabolite. Radioactivity in the ether soluble acidic fractions reached a maximum of 82% of the total in the tissue after 2 days. The level then decreased to 44% by the end of 24 days. A total of seven ether soluble components were detected. In addition to 2,4-D glutamic acid, which was detected in high amounts after 24 hours, 2,4-D aspartic acid was found to be the most abundant ether soluble metabolite after longer time periods. Mass spectral data and a fragmentation pattern are presented for 2,4-D aspartic acid.

Journal Article↗
PubMed1971

Indoleacetic Acid biosynthesis in Avena coleoptile tips and excised bean shoots.

Avena coleoptiles did not elongate when incubated with tryptophan under sterile conditions. Indole, anthranilic acid, and tryptamine promoted elongation. Under the same conditions, the tissue converted tryptophan-(14)C to IAA-(14)C. More IAA-(14)C was produced from indole-(14)C than from tryptophan-(14)C; however, the free tryptophan content of the tissue was also greatly increased by the indole treatment. Tryptophan-(14)C was readily taken up by the tissue but was mainly incorporated into protein and did not increase the free tryptophan level. When bean shoots were labeled with tryptophan-(14)C or indole-(14)C, the label incorporation into IAA-(14)C was very nearly the same. In this tissue the free tryptophan level in the tryptophan-(14)C and indole-(14)C treatments was also about equal. These results suggest that failure of exogenously supplied tryptophan to promote the elongation of Avena coleoptiles is a result of its predominant incorporation into protein and consequent unavailability for conversion to IAA.

Journal Article↗
PubMed1968

Light sensitivity of plastids and plastid pigments present in the albescent maize mutant.

Dark grown albescent corn seedlings are deficient in colored carotenoids but accumulate phytoene, phytofluene and an unidentified substance in the carotenol fraction. They bleach upon exposure to bright light and appear albino. Seedlings grown under low level incandescent light are normal in appearance and contain almost as much colored carotenoid as control seedlings. The existing leaf tissue of seedlings grown under low level light does not bleach upon exposure to bright light. The enhanced carotenoid synthesis and stabilization of plastids is not affected by brief illumination with red light but requires several hours of low level incandescent light.

Journal Article↗
PubMed1966

Dieldrin: extraction of accumulations by root uptake.

Certain forage crops can absorb and translocate the chlorinated hydrocarbon insecticide dieldrin from soil or sand. An extraction technique routinely used for analyses of residues does not quantitatively remove this internal chemical, but a method employing chloroform-methanol extraction leads to essentially quantitative recovery.

Absorption↗
PubMed1966

Isolation and morphology of temperature Agrobacterium tumefaciens bacteriophage.

Zimmerer, Robert P. (The Pennsylvania State University, University Park), Robert H. Hamilton, and Christine Pootjes. Isolation and morphology of temperate Agrobacterium tumefaciens bacteriophage. J. Bacteriol. 92:746-750. 1966.-Lysogeny was detected in 14 strains of Agrobacterium tumefaciens among 130 bacterial strains tested with strain B-6 used as the host. Partial lysis was observed with 13 additional bacterial strains. Morphological studies of five strains showed that the phage had similar features. A typical phage (Lv-1) had a polyhedralshaped head, approximately 71 by 63 mmu, and a tail, approximately 211 mmu by 9.5 mmu. The phage nucleic acid was found to be deoxyribonucleic acid. The bacteriophage have been designated L (for lysogenic) followed by the bacterial strain designation in lower case letters.

Bacteriophage Typing↗