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R H Hall

Publications and source records attributed to R H Hall.

At least 37 records · Page 2Linked to original sources
PubMed1992

Substrate specificities and properties of human phospholipases A2 in a mixed vesicle model.

Studies of the specificity of phospholipases A2 (PLA2s) for different substrates have usually been carried out in vesicles or mixed micelles, where differences in shape, size, or charge of vesicles formed with different phospholipids may give misleading results. Another factor is binding of the enzyme to the phospholipid surface, which has recently been addressed using vesicles of an anionic phospholipid, dimyristoyl-sn-glycero-3-phosphomethanol (DMPM) to which some extracellular PLA2s were shown to bind with a very high affinity (Jain, M. K., and Berg, O. G. (1989) Biochem. Biophys. Acta 1002, 127-156). In the present report we have used a similar system to study the substrate preferences of two human PLA2s that are thought to be physiologically relevant in the metabolism of arachidonic acid: a recombinant form of the human synovial fluid (14 kDa) PLA2 and the cytosolic (85 kDa) PLA2 found in monocytic cells. It is shown that both human enzymes bind tightly to DMPM vesicles and follow the basic characteristics of processive hydrolysis in this model using analysis of progress curves and substrate competition experiments. Mixed vesicles containing DMPM with small amounts (3-5 mol%) of other phospholipids have been used to study the substrate selectivity of the two human isoenzymes. The synovial fluid PLA2 shows a clear preference (approximately 7-fold) for sn-glycero-3-phosphoethanolamine over sn-glycero-3-phosphocholine. Within glycerophosphocholines, this enzyme displays little preference for the sn-2 fatty acyl group, and a slight preference for phospholipids with sn-1-acyl versus sn-1-alkyl substituents. In contrast, the cytosolic PLA2 shows a marked selectivity for arachidonoyl in the sn-2 position and only minor differences in selectivity for the polar head group in the sn-3 position. This enzyme does not distinguish between sn-1-acyl and sn-1-alkyl subclasses of glycerophosphocholines.

Arachidonic Acid↗
PubMed1992

Further consideration of the clonal nature of Salmonella typhi: evaluation of molecular and clinical characteristics of strains from Indonesia and Peru.

We examined envelope protein profiles, chromosomal restriction endonuclease digest patterns, and immune responses to envelope proteins for collections of Salmonella typhi strains isolated in Peru and Indonesia. Only minor differences in envelope protein patterns were apparent among strains. Strains from 7 of 20 Indonesian patients had a distinct chromosomal digest pattern compared with patterns of Peruvian and other Indonesian strains. Strains with this pattern carried the gene for the j flagellar antigen (H1-j); differences in response to envelope proteins of j and d strains were noted on immunoblot analysis. Our data suggest that there are genotypic and phenotypic differences among S. typhi strains. The clinical importance of these differences remains to be fully evaluated; however, in this study it was not possible to show a clear correlation between strain characteristics and disease severity.

Bacterial Proteins↗
PubMed1992

A new threat to public health: organochlorines and food.

Ambient levels of persistent toxic chemicals, chemicals that persist for decades in the environment, have reached levels high enough to affect the health of children. The organochlorines (PCBs, DDT and the dioxin family) accumulate in human adipose tissue. Pregnant women pass the contamination to their fetuses. The developing nervous system is the most vulnerable. Neurobehavioral deficits, including short-term memory loss, are detected in children born to mothers at the high end of the distribution curve of organochlorines. Humans are not alone in their susceptibility to these subtle effects. Wildlife exposed to the same spectrum of organochlorines as humans suffer a variety of behavioral changes. Rats and Rhesus monkeys fed diets containing the organochlorines under laboratory conditions exhibit behavioral changes that persist into adulthood. For humans, food provides 80 percent of organochlorine contamination. Meat, fish, dairy and commercial fruit are the main sources. A vegetarian diet including unsprayed fruit minimizes contamination. The ultimate solution to this public health problem is elimination of the organochlorines from the environment.

Animals↗
PubMed1991

Immunogenicity of Vibrio cholerae O1 toxin-coregulated pili in experimental and clinical cholera.

A functional tcpA gene, encoding the major subunit of toxin-coregulated pili (TCP), is necessary for Vibrio cholerae O1 Ogawa strain 395 to colonize the human intestine and confer protective immunity to virulent challenge. The immunogenicity of TCP and other antigens in experimental and naturally acquired cholera was determined. Seroconversion to cholera toxin (CT), whole cell preparations, and to Ogawa lipopolysaccharide but not to purified native TCP or to a TcpA mimiotope was found in volunteers. Local intestinal secretory immunoglobulin A from volunteers showed conversions to cholera toxin and lipopolysaccharide but not to TCP. Cholera patients in Indonesia showed a seroconversion rate to TCP of 3 of 6 and a seroconversion to a TcpA mimiotope of 1 of 6. Volunteer and patient sera showed similar vibriocidal seroconversions when assayed against either TCP-positive and TCP-negative V. cholerae O1 strains, suggesting that TCP do not contribute demonstrably to the vibriocidal antigen. We conclude that although seroconversion to TCP can occur in naturally acquired cholera, solid long-term protection can be engendered in the absence of a detectable anti-TCP immune response.

Amino Acid Sequence↗
PubMed1990

Vibrio cholerae HlyA hemolysin is processed by proteolysis.

The leukocidal activity of the Vibrio cholerae hemolysin (HlyA) was utilized to detect, enrich, and clone hybridoma cells expressing neutralizing monoclonal antibody in a new survivor selection protocol. A bank of 550 hybridoma clones was obtained from a mouse immunized with hemolysin by using standard techniques. The hybridoma bank was treated with a dose of HlyA hemolysin lethal to nonimmune clones. Five surviving hybridoma clones (X1 through X5) which possessed anti-HlyA activity were obtained. Western immunoblot analysis of V. cholerae culture supernatants with monoclonal antibody from clone X1 identified proteins with Mrs of 83,200, 71,600, and 60,300. Amino-terminal sequence analysis of the 71,600-Mr and 60,300-Mr forms showed homology with the published predicted sequence of HlyA. Our data indicate that proteolytic cleavage occurs between residues 120 and 121 (Glu-Leu) of the 83,200-Mr form, producing the 71,600-Mr form with the terminus NH2-L-L-F-T-P-F-D-Q-A-E-E-. Cleavage between residues 150 and 151 (Gly-Phe) releases the 60,300-Mr form with the terminus NH2-F-A-S-P-A-P-A-N-S-E-. Calculations based on the DNA sequence and the N termini indicated that the actual molecular masses of the 83,200-, 71,600-, and 60,300-Mr forms were, respectively, 79.4 kilodaltons (kDa), 68.6 kDa, and 65.3 kDa. Survivor selection and amino-terminal microsequencing offer powerful tools for the analysis of leukotoxic agents.

Amino Acid Sequence↗
PubMed1989

Significance of toxin-coregulated pili as protective antigens of Vibrio cholerae in the infant mouse model.

The infant mouse cholera model has been used to evaluate the relative importance of toxin-coregulated pili (TCP) as protective antigens of Vibrio cholerae 01. Electron microscopic and immunoblotting analyses revealed that, under the cultural conditions examined, TCP were only expressed by strains of classical biotype. Antibodies to TCP were sufficient to confer protection against two such strains, and were more efficient if the challenge vibrios were cultured for TCP expression. In contrast, such antibodies did not protect mice against challenge with any of four strains of El Tor biotype. Since two of the latter have previously been shown to possess non-lipopolysaccharide protective antigens, these results suggest that TCP are not the only such antigen in this model.

Animals↗
PubMed1989

Purification and analysis of colonization factor antigen I, coli surface antigen 1, and coli surface antigen 3 fimbriae from enterotoxigenic Escherichia coli.

Enterotoxigenic Escherichia coli fimbriae are immunogenic and play a key role in intestinal colonization. Native colonization factor antigen I, coli surface antigen 1, and coli surface antigen 3 fimbriae were purified by a common method involving shearing, differential centrifugation, gel filtration, and density gradient ultracentrifugation. The compositions and N-terminal sequences were determined. Coli surface antigen 3 possesses two N-terminal isoforms, one of which matches the published DNA sequence, except for the previously proposed signal sequence cleavage point.

Amino Acid Sequence↗
PubMed1988

Toxin, toxin-coregulated pili, and the toxR regulon are essential for Vibrio cholerae pathogenesis in humans.

Isogenic mutant strains of V. cholerae O1 lacking elements of a genetic regulon controlled by toxR and implicated in virulence were tested in volunteers. A deletion mutation in ctxA, the gene encoding the A subunit of cholera toxin, markedly attenuated disease symptoms without affecting intestinal colonization. Deletion of toxR, the gene encoding the cholera toxin-positive regulatory protein resulted in a diminution in colonizing capacity. A deletion mutation in tcpA, encoding the major subunit of the toxin coregulated pilus (regulated by toxR), abolished the colonizing capacity of this strain. These results show for the first time the role of a specific pilus structure in colonization of the human intestine by V. cholerae O1 and exemplify the significance of a genetic regulon in pathogenesis.

Adult↗
PubMed1988

Morphological studies on fimbriae expressed by Vibrio cholerae 01.

Colonization of the small intestine is an essential step in the pathogenesis of Vibrio cholerae diarrhea. At least one type of fimbriae, known as TcpA are required for the colonization process. This paper reports electron microscopic evidence that V. cholerae strains can express at least two other fimbrial types. Classical strains express three types: TcpA fimbriae are 5-6 nm in diameter and form bundles of parallel undulating filaments up to 15 micron long; Type B are 3 nm wide and of wavy morphology, and Type C are rigid, isolated filaments 5-6 nm wide and 180-800 nm long. El Tor strains express fimbriae resembling Types B and C. Types B and C were also found on a tcpA- isogenic mutant of V. cholerae 395 N1, and are thus encoded by genetically distinct loci. TcpA fimbriae, but not Types B or C, were labeled with gold-conjugated anti-TcpA antibody. Four El Tor strains, including two environmental isolates that poorly colonize humans, expressed fimbriae resembling Types B and C, but did not express TcpA. Multiple types of fimbriae may represent colonization factors for surfaces present in the environment and in the human gut. Characterization of the role of fimbriae in immunogen presentation and immunity could facilitate the improvement of cholera vaccines.

Cholera↗
PubMed1981

Measles virus antibodies in a laboratory colony of owl monkeys (Aotus trivirgatus).

Serologic testing revealed that 17/84 (20.2%) of bought-in Aotus and 1/31 (3.2%) of colony-born Aotus had haemagglutination-inhibition antibody. Clinically-inapparent measles infections were detected in 3 monkeys by increased antibody titres. Following the detection of a recent infection, antibody titre persisted at a high level for at least 240 days. Although 84% of the monkeys were sero-susceptible, no further serological evidence of measles infection occurred.

Animals↗
PubMed1976

Hormonal mechanisms for differentiation in plant tissue culture.

Cells possess extraordinary powers to organize their molecular processes not only to maintain a cell in a given steady state but also to recognize that state during differentiation. Regulation of these organizational forces appears to be under the control of chemical factors, and a hormonal concept of regulation has evolved. Hormones have been considered to act by reacting with a specific target site. This may be part of their mode of action, 0ut i would like to suggest that a hormone enters and becomes part of a total molecular resonance system. In so doing, the entire molecular system of the cell is modified.

Cell Differentiation↗
PubMed1975

A high molecular weight RNA fraction in chromatin.

Utilizing a new chromatin isolation and fractionation technique we have obtained a high molecular weight RNA fraction from L-929 cell chromatin. The synthesis of this RNA is not greatly inhibited by concentrations of 0.04 mug/ml actinomycin D in the medium. Its synthesis appears to be strongly inhibited by 2 mug/ml of alpha-amanitin. The RNA appears to be quickly degraded (or removed from the chromatin) and does not contain a poly(A) sequence at its 3'-OH terminal end. Our working hypothesis is that this RNA is "nascent" heterogenous nuclear RNA partially transcribed from regions of the chromatin.

Adenine Nucleotides↗