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Biomedical subjects

A Cheung

Publications and source records attributed to A Cheung.

At least 91 records · Page 5Linked to original sources
PubMed1986

Immunization with synthetic peptides of a Plasmodium falciparum surface antigen induces antimerozoite antibodies.

Polypeptides expressed on the surface of merozoites, the invasive stage of the asexual blood cycle, are good candidates for the development of malaria vaccines. Five synthetic peptides with predetermined specificity deduced from a genomic DNA clone coding for the NH2-terminal portion of the main merozoite surface polypeptide of Plasmodium falciparum were evaluated for their capability to raise antibodies that react with the P. falciparum merozoites. Antibodies induced by two of the peptides (3 and 5) reacted with the membrane surfaces of seven of seven isolates of P. falciparum from different geographic areas. Antibodies against peptide 4, which contains a repeated amino acid sequence (Gly-Gly-Ser and Val-Ala-Ser), reacted with six of seven isolates. Structural analysis of the deduced polypeptides suggests that peptide 3 is exposed at the surface of merozoites. When it was used to immunize monkeys, three of the four animals were partially protected from a challenge infection that induced a fulminant infection in control animals.

Amino Acid Sequence↗
PubMed1986

Localization of human pituitary hormones by multiple immunoenzyme staining procedures using monoclonal and polyclonal antibodies.

Mouse monoclonal and rabbit polyclonal antibodies to human pituitary hormones were applied together to sections of normal and neoplastic human pituitary tissue. Binding sites were revealed with species-specific immune reagents combined with various enzymes (peroxidase, alkaline phosphatase, and beta-D-galactosidase). The enzymes were developed separately to give differently colored end-products. Where two hormones were present in the same cell, a mixed color was produced. Up to four hormones could be immunostained in a single section. Multiple immunoenzymatic staining has great potential for the analysis of plural antigen production by single cells and relationships between cells producing different antigens.

Animals↗
PubMed1986

Serotoninergic inhibition of LH secretion in the domestic fowl.

Immature cockerels were injected with drugs known to affect serotoninergic activity. The receptor agonist quipazine as well as pargyline, an inhibitor of serotonin breakdown, both reduced plasma LH concentrations in a time-dependent fashion. The effect of pargyline was also dose-related. The serotonin precursor, tryptophan, reduced plasma LH levels. Tryptophan and pargyline were as effective in pubertal cockerels as in 3-week-old birds. Responses to quipazine were attenuated by the antagonist, methysergide, although another antagonist, cyproheptadine, also reduced plasma LH levels. Serotonin itself had no effect on plasma LH levels. Parachlorophenylalanine, which blocks serotonin synthesis, had no effect on plasma LH by itself, but attenuated the tryptophan-induced inhibition of LH. These data indicate that serotoninergic mechanisms inhibit secretion of LH in domestic fowl. This mechanism probably operates through the central nervous system.

Animals↗
PubMed1986

Defined Plasmodium falciparum antigens in malaria serology.

The study evaluates three enzyme-linked immunosorbent assays (ELISA) of malaria antigens suitable for use in large-scale epidemiological studies. Results obtained using sera from 567 persons from the Gambia indicated that the micro-ELISA method using parasitized red blood cell extract did not reliably quantitate antimalarial antibodies, especially in young children. In contrast, two micro-ELISA methods that employed purified, defined antigens (a polypeptide of M(r) = 41 000 present in rhoptries, and a 31-1 fusion polypeptide corresponding to a merozoite surface antigen) permitted the precise determination of antimalarial antibodies in both adults and children. Problems and advantages associated with the use of the M(r) = 41 000 and 31-1 antigens for the determination of antimalarial antibodies are discussed.

Antigens, Protozoan↗
PubMed1986

Purpura fulminans in a Chinese boy with congenital protein C deficiency.

Severe and recurrent purpura fulminans developed in a Chinese boy at one day of age. Results of coagulation studies performed on the patient during attacks were compatible with the diagnosis of disseminated intravascular coagulation. Subsequent investigations have revealed that the patient is homozygous and that his parents are heterozygous for protein C deficiency. Cryoprecipitate and fresh frozen plasma induced a remission, and administration of warfarin has been successful in preventing recurrence of attacks for as long as 8 months without infusion of any plasma components. None of the family members who are heterozygous for protein C deficiency have had thrombotic episodes.

Combined Modality Therapy↗
PubMed1985

Cloning and expression in Escherichia coli of a surface antigen of Plasmodium falciparum merozoites.

A complementary DNA library was constructed from mRNA purified from asexual blood forms of Plasmodium falciparum. Among the members of this library we have identified a plasmid (pMC31-1) coding for a polypeptide exposed at the surface of merozoites, the invasive stage of the asexual cycle. This plasmid was identified by direct expression using both polyclonal and monoclonal antibodies specific for a schizont polypeptide of 200 kd which has been shown to be processed to an 83-kd polypeptide expressed at the surface of merozoites. The cDNA portion of the pMC31-1 plasmid hybridizes with DNA from three isolates of P. falciparum. Antisera raised against extracts of Escherichia coli harbouring pMC31-1 react with surface and internal structures of schizonts and with the surface of merozoites from all the isolates of P. falciparum examined. These results suggest that plasmid pMC31-1 encodes an antigen of value for the development of a vaccine against malaria.

Amino Acid Sequence↗
PubMed1985

Distribution of galanin immunoreactivity in the respiratory tract of pig, guinea pig, rat, and dog.

Galanin, a newly discovered peptide isolated from porcine intestine, is known to cause contraction in rat smooth muscle preparations and to induce hyperglycaemia in dogs. By the use of radioimmunoassay and immunohistochemical techniques the concentration and distribution of galanin immunoreactivity were determined in several areas of the respiratory tract of five dogs, five guinea pigs, five rats, and two pigs. Antibodies were raised in rabbits to whole unconjugated natural porcine galanin. The highest galanin concentrations were found in the bronchus and the trachea of the dog, guinea pig, rat (2 pmol/g in each case), and pig (less than 1 pmol/g). The lowest galanin concentrations were found in the lung parenchyma. Gel chromatographic analysis in the pig showed one molecular form of galanin coeluting with the porcine galanin standard. By means of the indirect immunofluorescence technique on sections of tissues fixed in benzoquinone solution, galanin was found to be confined to nerve fibres in different regions of the respiratory tract. In the nasal mucosa of the pig nerve fibres containing galanin were distributed around seromucous glands and blood vessels and beneath the epithelium. In the trachea, bronchus, and major intrapulmonary airways of the pig, dog, and guinea pig galanin immunoreactive fibres were detected predominantly in smooth muscle, as well as around seromucous glands and in the adventitia of blood vessels. Rarely, galanin immunoreactive nerve fibres were found in the lung parenchyma. A few galanin immunoreactive ganglion cells also containing vasoactive intestinal polypeptide were found in the adventitia of the tracheobronchial wall of the pig and dog. The distribution of galanin suggests that it may have some influence on airway, vascular, and secretory functions in the mammalian respiratory tract.

Animals↗
PubMed1984

Nucleotide sequence of the VP1 gene of the foot-and-mouth disease virus strain A Venceslau.

The VP1 coat protein of FMDV strain A Venceslau (Aven) consists of 213 amino acid residues. Serum neutralization tests demonstrated that strain Aven is closely related to strain A Argentina/79 (A79) but significantly different from strain A24Cruzeiro (A24). There is a strong correlation between the amino acid sequences and the serological data. Nucleotide and amino acid sequence analyses of VP1 showed that serologically related viruses (Aven and A79) differ less in this region of the genome than those of serologically distinct viruses (Aven vs. A24). The most significant variation between Aven and A24 occurs at amino acid positions 43 to 46, in which all four residues are different.

Amino Acid Sequence↗
PubMed1984

Inhibition of luteinizing hormone (LH)-releasing hormone-induced secretion of LH in rat anterior pituitary cell culture by testosterone without conversion to 5 alpha-dihydrotestosterone.

The role of 5 alpha-reduction of testosterone in the inhibition of LH secretion was investigated in rat anterior pituitary cell cultures. Pituitary cells were preincubated with testosterone or dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one) for 17 h and then with LHRH for an additional 4 h. Dihydrotestosterone was 6-fold more potent than testosterone in the inhibition of LHRH-induced LH release. Basal LH secretion was not affected by either androgen. The inhibition curves of testosterone and dihydrotestosterone were not shifted by the presence of the 5 alpha-reductase inhibitors 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one (4-MA) and 17 beta-N,N-diisopropylcarbamoyl-4-aza-androstan-3-one (DIPA). Neither 4-MA nor DIPA alone had an effect on either basal or LHRH-induced LH release. When pituitary cells were incubated with [3H]testosterone for 17 h, the radioactivities were found to be unmetabolized testosterone (66.9 +/- 2.4%), dihydrotestosterone (13.3 +/- 0.5%), androstenedione (15.9 +/- 1.3%), 5 alpha-androstane-3,17-dione (2.8 +/- 0.3%), and 3 alpha (beta), 17 beta-androstanediol (less than 1%). In the presence of 4-MA or DIPA, 5 alpha-reduction of testosterone was completely inhibited; androstenedione was the only metabolite. Androstenedione was only 12% as potent as testosterone in the inhibition of LHRH stimulation of LH release, and conversion of [3H]androstenedione to testosterone and dihydrotestosterone did occur in these cells. When [3H]dihydrotestosterone was incubated with pituitary cells, the radioactivities were dihydrotestosterone (64.4 +/- 0%), 5 alpha-androstanedione (19.3 +/- 1%), 3 alpha (beta), 17 beta-androstanediol (7.7 +/- 1.7%), and unknown polar metabolites. 4-MA and DIPA had no effect on the metabolism of dihydrotestosterone. These results indicate that both testosterone and dihydrotestosterone inhibit LHRH-induced LH release and that this activity of testosterone does not depend on its 5 alpha-reduction.

5-alpha Reductase Inhibitors↗
PubMed1984

Misaminoacylation by glutaminyl-tRNA synthetase: relaxed specificity in wild-type and mutant enzymes.

Escherichia coli glutaminyl-tRNA synthetase (GlnRS) (EC 6.1.1.18) is a monomeric polypeptide of 553 amino acids. Its amino acid sequence and its gene (glnS) sequence are known. A structural gene mutation, glnS7, codes for a mischarging GlnRS, which acylates some noncognate tRNA species (e.g., su+3 tRNATyr) with glutamine. The mutant enzyme was shown to catalyze in vitro the acylation of glutamine to su+3 tRNATyr, but not to wild-type tRNATyr. The mutation responsible produces an amino acid change in the amino-terminal half of the enzyme. Unexpectedly, overproduction of wild-type GlnRS also leads to in vivo mischarging of su+3 tRNATyr. In vitro and in vivo studies have not revealed evidence for an attenuation or autogenous regulation mechanism for GlnRS, but have implicated transcriptional and translational control in the expression of this enzyme.

Amino Acid Sequence↗
PubMed1983

RNA encoded by the IR1-U2 region of Epstein-Barr virus DNA in latently infected, growth-transformed cells.

The IR1-U2 region of Epstein-Barr virus DNA consists of multiple copies of a 3.1-kilobase (kb) repeat sequence, IR1, which maps to the left of a 3.3-kb unique region, U2. Although hybridizations of cytoplasmic polyadenylated RNA from latently infected cells to viral DNA indicate that the IR1-U2 region encodes a substantial fraction of the viral RNA in these cells, only a single low-abundance 3-kb cytoplasmic polyadenylated RNA has been identified on Northern blots. Further analysis of the cytoplasmic polyadenylated RNA encoded by the IR1-U2 region indicates that (i) the RNA is transcribed from left to right; (ii) there are only three copies of the 3-kb RNA per cell; and (iii) the RNA is spliced. The RNA hybridizes to possibly contiguous 0.56- and 1.3-kb U2 domains. These domains and part of IR1 hybridize to the 3-kb cytoplasmic RNA. DNA between IR1 and the 0.56-kb U2 domain does not hybridize to the 3-kb RNA. The CCAAT-34 nucleotide-TATAA sequence in IR1 may be part of the promotor for the 3-kb cytoplasmic polyadenylated RNA since (i) it enables left-to-right transcription of IR1 by a HeLa cell extract, and (ii) latently infected cells contain giant polyadenylated nuclear RNAs which differ in size by 3 kb, as would be expected if transcription initiates in any copy of IR1 and continues through the rightward remaining copies into U2.

Cell Line↗
PubMed1983

Comparison of the major antigenic determinants of different serotypes of foot-and-mouth disease virus.

Complete nucleotide sequences which code for the capsid protein VP1 of two foot-and-mouth disease virus serotypes, O1Campos/Brazil/58 and C3Indaial/Brazil/71, have been determined. Ten available VP1 sequences (three serotype O, three serotype C, and four serotype A) were aligned and compared. Our evidence suggests that O1BFS/Britain/68 and O1K/Germany/66 are closely related to O1Campos/Brazil/58. Significant variations were observed between the nucleotide sequences of C3Indaial determined by two different laboratories. These differences are probably the result of virus adaptation and propagation in different laboratories. In one of the isolates (C3Biogen), a 13-base-pair stem and 13-base-pair loop structure is located in the 134-158 amino acid variable region. Isolates of different serotypes differ at two highly variable regions, amino acid positions 42-60 and 134-158, but isolates of the same serotype show major differences only in the variable region between amino acids 134 and 158. Since the remaining amino acid sequence of VP1 is highly conserved, we conclude that the 134-158 amino acid variable region is involved in subtype specificity, whereas both variable regions contribute to serotype differences.

Amino Acid Sequence↗
PubMed1983

Binding of a 4-methyl-4-aza-steroid to 5 alpha-reductase of rat liver and prostate microsomes.

A tritium labeled 5 alpha-reductase inhibitor, [1,2-3H] 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one ([3H]4-MA), binds reversibly to a high affinity site (Kd, 6.5 nM) in liver microsomes from male rats. The binding requires a nicotinamide nucleotide coenzyme; NADH is at least 100 times less potent than NADPH, and NADP+, NAD+, flavin adenine dinucleotide, coenzyme A, and ADP are inactive. The relative potencies of 13 steroids as inhibitors of the binding of [3H]4-MA to liver microsomes correlate with their relative potencies as inhibitors of the conversion of [14C]testosterone to [14C]5 alpha-dihydrotestosterone by liver microsomes. Comparison of liver microsomes from mature female rats and microsomes from mature male rat liver, ventral prostate, spleen, kidney, and skeletal muscle shows that their NADPH-dependent [3H]4-MA binding capacities correlate with their levels of 5 alpha-reductase activity. These results suggest that [3H]4-MA binds specifically to 5 alpha-reductase in a NADPH-dependent manner. 5 alpha-Reductase was solubilized from liver microsomes with a detergent, Lubrol-WX, and the solubilized enzyme also binds [3H]4-MA. The relative potencies of 13 steroids as inhibitors of rat ventral prostate and liver 5 alpha-reductase are the same, strongly suggesting that the 5 alpha-reductases in the two tissues are the same.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1982

Escherichia coli glutaminyl-tRNA synthetase. I. Isolation and DNA sequence of the glnS gene.

We have isolated a lambda-transducing phage carrying the gene (glnS) for Escherichia coli glutaminyl-tRNA synthetase. The location of the glnS gene within the 13.5-kilobase E. coli DNA transducing fragment was determined by genetic means. The glnS gene was recloned into plasmid pBR322 and its nucleotide sequence was established. The DNA sequence translates to a protein of 550 amino acids.

Amino Acyl-tRNA Synthetases↗
PubMed1982

Escherichia coli glutaminyl-tRNA synthetase. II. Characterization of the glnS gene product.

Glutaminyl-tRNA synthetase has been purified by a simple, two-column procedure from an Escherichia coli K12 strain carrying the glnS structural gene on plasmid pBR322. The primary sequence of this enzyme as derived from the DNA sequence (see accompanying paper) has been confirmed. Manual Edman degradation was used to identify the NH2-terminal sequence of the protein. Oligopeptides scattered throughout the primary sequence of glutaminyl-tRNA synthetase were sequenced by the gas chromatographic-mass spectrometric method and matched to the theoretical peptides derived from the translated DNA sequence. The expected carboxyl terminus at position 550 was verified by carboxypeptidase B digestion. The primary sequence of glutaminyl-tRNA synthetase contains no extensive sequence repeats. A search was made for sequence homologies between this enzyme and the few other aminoacyl-tRNA synthetases for which primary sequences are available. A single homologous region is shared by at least three of the synthetases examined here.

Amino Acid Sequence↗
PubMed1982

Mechanochemical coupling in the relaxation of rigor-wave sea urchin sperm flagella.

The relaxation (straightening) of flagellar rigor waves, which is known to be induced by micromolar ATP concentrations was investigated with respect to its dependence on the binding and hydrolysis of ATP. Flagellar rigor waves were formed by the dilution of demembranated, reactivated sea urchin (Lytechinus pictus) spermatozoa into ATP-free buffer. Relaxation in response to nucleotide was quantitated by measuring theta, the mean flagellar bend angle per sperm; this novel assay permitted determination of the rate of relaxation. It was found that (a) the rate of flagellar relaxation induced by 4 X 10(-6) M ATP was inhibited 80% by vanadate concentrations of 3 X 10(-6) M and above; (b) of 16 hydrolyzable and nonhydrolyzable nucleotide di-, tri-, and tetraphosphates tested, only three, each of which was hydrolyzed by the flagellar axonemal ATPase activity (ATP, dATP, and epsilon-ATP) were also capable of effecting relaxation; (c) several hundred ATP molecules were estimated to be hydrolyzed by each dynein of ATP hydrolysis, which defines the efficiency of ATP utilization, increased 30-fold as the ATP relaxation depends on ATP hydrolysis; (b) because it depends on ATP hydrolysis, flagellar relaxation is an inappropriate model system for investigating the role of ATP binding in the mechanochemical cycle of dynein; and (c) the efficiency of mechanochemical coupling in flagellar motility is an ATP-dependent phenomenon. A general model of relaxation is proposed based on active microtubule sliding.

Adenine Nucleotides↗