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H E Paaren

Publications and source records attributed to H E Paaren.

10 recordsLinked to original sources
PubMed1990

Strain-Specific Inhibition of nod Gene Induction in Bradyrhizobium japonicum by Flavonoid Compounds.

A broad-host-range plasmid, pEA2-21, containing a Bradyrhizobium japonicum nodABC'-'lacZ translational fusion was used to identify strain-specific inhibitors of the genes required for soybean nodulation, the common nod genes. The responses of type strains of B. japonicum serogroups USDA 110, USDA 123, USDA 127, USDA 129, USDA 122, and USDA 138 to nod gene inhibitors were compared. Few compounds inhibited nod gene expression in B. japonicum USDA 110. In contrast, nod gene expression in strains belonging to several other serogroups was inhibited by most of the flavonoids tested. However, the application of two of these strain-specific compounds, chrysin and naringenin, had little effect on the pattern of competition between indigenous and inoculum strains of B. japonicum in greenhouse and field trials. Preliminary studies with radiolabeled chrysin and naringenin suggest that the different responses to nod gene inhibitors may be partly due to the degree to which plant flavonoids can be metabolized by each strain.

Journal Article↗
PubMed1987

Induction of Bradyrhizobium japonicum common nod genes by isoflavones isolated from Glycine max.

The early events in legume nodulation by Rhizobium spp. involve a conserved gene cluster known as the common nod region. A broad-host-range plasmid (pEA2-21) containing a Bradyrhizobium japonicum nodDABC-lacZ translational fusion was constructed and used to monitor nod gene expression in response to soybean root extract. Two inducing compounds were isolated and identified. Analysis using ultraviolet absorption spectra, proton nuclear magnetic resonance, and mass spectrometry showed that the two inducers were 4',7-dihydroxyisoflavone (daidzein) and 4',5,7-trihydroxyisoflavone (genistein). Induction was also seen with some, but not all, of the flavonoid compounds that induce nod genes in fast-growing Rhizobium strains that nodulate clover, alfalfa, or peas. When pEA2-21 was introduced into Rhizobium trifolii, it was inducible by flavones but not by daidzein and genistein. In Rhizobium fredii, pEA2-21 was induced by isoflavones and flavones. Thus, the specificity of induction appears to be influenced by the host-strain genome.

Journal Article↗
PubMed1986

Nucleic acid quantitation by continuous flow fluorometry.

A system for rapid and sensitive fluorometric measurement of nucleic acids is described. Samples can be analyzed virtually as fast as they can be injected into the analyzer (three to five per minute). 5-microliter samples ranging in concentration from 0.05 to 40 micrograms/ml can be measured accurately. The sample can easily be recovered.

Autoanalysis↗
PubMed1984

Metabolism of 25-hydroxyvitamin D3 by rat kidney cells in culture: isolation and identification of cis- and trans-19-nor-10-oxo-25-hydroxyvitamin D3.

A primary confluent culture of epithelial cells from rat kidney has been developed. These cells possess a 3.2-3.4 S high-affinity, low-capacity binding protein for 1,25-dihydroxyvitamin D3. They metabolize 25-hydroxyvitamin D3 to at least five metabolites. Two have been identified as 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3. Two others have been identified by means of physical data and cochromatography as trans 19-nor-10-oxo-25-hydroxyvitamin D3 and the other as its cis isomer. These two "metabolites" have not been observed in vivo, but one of them (cis) comigrates with 1,25-dihydroxyvitamin D3 on straight-phase high-performance liquid chromatography. Thus, mere cochromatography on high-performance liquid chromatography is not sufficient to identify critical vitamin D metabolites.

Animals↗
PubMed1980

In vivo and in vitro inhibition of rat liver vitamin D3-25-hydroxylase activity by 19-hydroxy-10(S),19-dihydrovitamin D3.

Rats treated with varying amounts of 19-hydroxy-10(S),19-dihydrovitamin D3 prior to administration of physiologic doses of vitamin D3 exhibit normal intestinal calcium transport but are unable to mobilize bone calcium. In contrast, 19-hydroxy-10(R),19-dihydrovitamin D3 had no inhibitory activity. Circulating serum levels of 25-hydroxy[3H]vitamin D3 and 1 alpha, 25-dihydroxy[3H]vitamin D3 are markedly suppressed but not totally eliminated in animals predosed with 19-hydroxy-10(S),19-dihydrovitamin D3 before [3H]vitamin D3. Hepatic 25-hydroxy[3H]vitamin D3 levels were approximately equal in both 19-hydroxy-10(S),19-dihydroviotamin D3 treated and untreated rats. However, the rate of conversion of [3H]vitamin D3 to 25-hydroxyvitamin D3 in vivo is greatly reduced in the treated rats. The inhibitory vitamin analogue was also show to block hepatic microsomal 25-hydroxylation in vitro. These results indicate that 19-hydroxy-10(S),19-dihydrovitamin D3 is a specific inhibitor for a hepatic microsomal vitamin D3-25-hydroxylase system.

Animals↗
PubMed1980

Role of kidney tissue in the production of 25-hydroxyvitamin D3-26,23-lactone and 1 alpha, 25-dihydroxyvitamin D3-26,23-lactone.

Labeled 25-hydroxyvitamin D3-26,23-lactone was isolated from the serum of vitamin D-repleted rats given [3 alpha-3H]-25-hydroxyvitamin D324 hr prior to sacrifice. The metabolite was identified by cochromatography with the authentic lactone on straight-phase and reversed-phase high-performance liquid chromatography. Production of the lactone was abolished by nephrectomy indicating that the kidney is the site of synthesis. Homogenate of kidneys from chickens given large doses of vitamin D can carry out in vitro production of the lactone from 25-hydroxyvitamin D3. When 1 alpha, 25-dihydroxyvitamin D3 was used as substrate, this system produced only traces of a compound believed to be 1 alpha, 25-dihydroxyvitamin D3-26,23-lactone. However, incubation of rachitic chicken kidney homogenates with 25-hydroxyvitamin D3-26,23-lactone produced substantial amounts of a compound that has been identified by mass spectrometry as 1 alpha, 25-dihydroxyvitamin D3-26,23-lactone. Thus, the development of a functional group on C-26 and eventual lactone formation takes place in kidney by a system acting on 25-hydroxyvitamin D3.

Animals↗
PubMed1978

Direct C-1 hydroxylation of vitamin D compounds: convenient preparation of 1alpha-hydroxyvitamin D3, 1alpha, 25-dihydroxyvitamin D3, and 1alpha-hydroxyvitamin D2.

An efficient procedure for the direct C-1 hydroxylation of vitamin D compounds has been developed. The method involves conversion of vitamin D3 tosylates to 3,5-cyclovitamin D derivatives, allylic oxidation with selenium dioxide, and acid-catalyzed solvolysis to the 1 alpha-hydroxyvitamin D analogs. When applied to vitamin D3,25-hydroxyvitamin D3, and vitamin D2, this sequence give the corresponding 1alpha-hydroxylated derivatives in 10-15% yield.

Cholecalciferol↗