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Biomedical subjects

P C Tai

Publications and source records attributed to P C Tai.

14 recordsLinked to original sources
PubMed1992

Circulating histamine and eosinophil cationic protein levels in nocturnal asthma.

1. To investigate the role of mast cells and eosinophils in the pathogenesis of nocturnal asthma, the plasma methylhistamine concentration, serum eosinophil cationic protein level and peak expiratory flow rate were measured 2-hourly for 24 h in 10 patients with nocturnal asthma and in 10 healthy control subjects. Nocturnal asthma was defined as at least one nocturnal awakening per week due to cough, wheeze or breathlessness with an average overnight fall in peak expiratory flow rate of at least 15% during a 2-week run-in period. 2. The lowest peak expiratory flow rate occurred at 02.00-04.00 hours in the group with nocturnal asthma, whose overnight fall in peak expiratory flow rate was 29 +/- 5% in comparison with 5 +/- 1% (means +/- SEM) in the normal subjects. 3. Plasma methylhistamine levels at night (0.200-04.00 hours) were lower than during the day (10.00-20.00 hours) in both asthmatic patients and normal subjects (asthmatic patients: day, median 0.22 ng/ml, 95% confidence intervals 0.18-0.34 ng/ml; night, 0.17 ng/ml, 0.13-0.24 ng/ml; P < 0.01; normal subjects: day, 0.31 ng/ml, 0.24-0.41 ng/ml; night, 0.24 ng/ml, 0.21-0.33 ng/ml; P < 0.01). 4. The serum eosinophil cationic protein level was higher by day (30 ng/ml, 8-47 ng/ml) than by night (21 ng/ml, 5-34 ng/ml; P < 0.04) in the group with nocturnal asthma, but did not change significantly with the time of day in the normal subjects (day: 8 ng/ml, 4-14 ng/ml; night: 8 ng/ml, 5-21 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1979

Triphasic concentration effects of gentamicin on activity and misreading in protein synthesis.

Gentamicin is shown to exert a triphasic concentration effect on peptide synthesis in vitro with natural messengers. Low concentrations (up to 2 micron) caused slowing and a decrease in total synthesis, but little misreading (assayed with extracts lacking Glu-tRNA); the inhibition was greater with an initiating system (with phage RNA as messenger) than with pure chain elongation on purified endogenous polysomes of Escherichia coli. Moderate concentrations (up to 100 micron) slowed synthesis less, markedly increased its duration in the noninitiating system, and strongly stimulated misreading; at optimal concentrations total synthesis was even greater than normal. Moreover, with phage RNA these concentrations increased the synthesis of large polypeptides. We conclude that binding of gentamicin to its first site causes inhibition but little misreading; binding to additional site(s) partly reverses the inhibition by first-site binding and markedly stimulates misreading, and the misreading appears to favor "readthrough" of termination codons. In the third phase (greater than 100 micron) synthesis is slowed again but the pattern of misreading does not appear to be altered; this effect need not involve a specific further action on the ribosome.

Bacterial Proteins↗
PubMed1979

Extracellular labeling of growing secreted polypeptide chains in Bacillus subtilis with diazoiodosulfanilic acid.

Studies of the mechanism of protein secretion in a Gram-positive bacterium, Bacillus subtilis, yielded results very similar to those previously obtained with a Gram-negative organism: nascent chains protruding from protoplasts could be labeled extracellularly; the labeled chains could be recovered on polysomes isolated from the membrane--polysome fraction; they could be released by puromycin, low Mg2+, or chain completion; the completed chains include a known secreted protein (alpha-amylase); and their ribosomes appear to be attached to membrane solely by their nascent chains. The reagent used for extracellular labeling, [1252]diazoiodosulfanilic acid, yielded severalfold more specific labeling of the nascent chains (7--10% of the total cellular labeling and one-fourth to one-third of that of the membrane--polysome fraction) than was obtained earlier with another nonpenetrating reagent.

Amylases↗
PubMed1978

Streptomycin causes misreading of natural messenger by interacting with ribosomes after initiation.

The induction of misreading by streptomycin in vitro, previously observed with synthetic messengers, is now demonstrated with natural (endogenous or viral) messenger by the use of extracts of temperature sensitive mutants lacking Glu--tRNA or Val--tRNA synthetase. With chain-elongating but noninitiating ribosomes (i.e., purified polysomes) deprived of an aminoacyl--tRNA, streptomycin and other aminoglycosides, over a wide range of concentrations, stimulate incorporation. With ribosomes initiating in the presence of streptomycin stimulation is also observed but it is restricted, just like phenotypic suppression in cells, to very low streptomycin concentrattions which evidently allow some ribosomes to initiate and later encounter them in the course of chain elongation. The stimulation is accompanied by an increase in the size of the products; hence, it is evidently due to substitution of an incorrect aminoacyl--tRNA for a missing one. The test introduced here also has revealed a misreading effect of streptomycin on resistant ribosomes. In addition, significant intrinsic misreading was observed without streptomycin, indicating that under optimal conditions for in vitro protein synthesis an empty codon is frequently read by an incorrect aminoacyl--tRNA.

Anti-Bacterial Agents↗
PubMed1978

Interaction of secreted nascent chains with surrounding membrane in Bacillus subtilis.

To determine the length of secreted nascent polypeptide chain that is surrounded by membrane, we digested labeled nascent chains protruding from protoplasts of Bacillus subtilis with Pronase and isolated the residual ribosome-attached chains from the membrane-polysome fraction. Gel chromatography revealed a sharp major peak that had been protected by membrane plus bound ribosomes. The ribosomes themselves protected half as great a length. Because no free chain between the ribosome and the membrane was detected by Pronase treatment, the difference between the two protected lengths should measure the length protected by the membrane. More accurate measurements of these lengths, obtained by dansylation of the exposed NH2 terminus of the isolated fragments, yielded a difference of 21 amino acids. This value corresponds to an extended chain of 75 A, which is approximately the thickness of the bacterial cell membrane. We earlier presented evidence that bacterial ribosomes are attached to membrane solely by their secreted chain. The present results further show that after loss of the extracellular segment of the chain its attachment persists, at 37 degrees as well as 0 degrees C. These findings suggest that the chain does not slip through a passive membrane but is actively held within a channel.

Amino Acid Sequence↗
PubMed1978

Nascent peptide as sole attachment of polysomes to membranes in bacteria.

When membrane-polysome complexes from Escherichia coli were treated with puromycin, at various Mg2+ and K+ concentrations, the bulk of the ribosomes were released from the membrane. Moreover, many released ribosomes released ribosomes remained attached to mRNA (pseudopolysomes). These results suggest that ribosomes are attached to the membrane in bacteria solely by their nascent chain. Without a direct attachment the conformational changes associated with chain elongation on the ribosome cannot force the growing chain through the membrane, and so alternative sources of energy for the transfer must be considered.

Bacteria↗
PubMed1977

What eosinophils do.

Explore the source record for details and available documents.

Binding Sites, Antibody↗
PubMed1977

Extracellular labeling of nascent polypeptides traversing the membrane of Escherichia coli.

To provide direct evidence for the hypothesis that secreted proteins may traverse membranes as growing chains, we labeled spheroplasts of Escherichia coli with a reagent (acetyl[35S]methionyl methylphosphate sulfone) that reacts with amino groups but does not cross the membrane. After fractionation, about 6% of the label in the membrane-polysome fraction was found to be attached to the polysomes. This attachment was via peptidyl-tRNA, as shown by several tests: release of most of the label from purified polysomes at low Mg2+; subsequent loss of about 25,000 daltons on cleavage by dilute alkali; release by puromycin; and release, accompanied by a marked increase in average molecular weight, on peptide chain completion. Moreover, a significant fraction of the completed chains was identified serologically and by molecular weight as a major periplasmic protein, alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum); EC 3.1.3.1]. This work provides direct evidence that: (i) secreted proteins thread through the membrane as growing peptide chains; and (ii) membrane-associated polysomes in bacteria are functionally attached to membrane and not merely trapped on disruption of the cell.

Alkaline Phosphatase↗
PubMed1977

DNA-directed synthesis in vitro of beta-galactosidase: requirement for a ribosome release factor.

The DNA-directed synthesis of beta-galactosidase in Escherichia coli extracts has been investigated in a partially fractionated system. A dependency was obtained for 3',5'-cyclic AMP receptor protein and also for a factor, from the salt wash of ribosomes, that has been purified to near homogeneity. This factor has been identified with a ribosome release factor previously purified from the supernatant fraction by A. Hirashima and A. Kaji [(1972) Biochemistry 11,4037-4044]. In the coupled transcription-translation system this factor stimulates beta-galactosidase synthesis and total protein synthesis 2- to 4-fold. It is thus clear that the ribosome release factor has a physiological function in translation. It may also affect transcription, because it stimulated total RNA synthesis up to 50% in this in vitro system.

Cross Reactions↗
PubMed1977

Purification of normal human eosinophils using the different binding capacities of blood leucocytes for complexed rabbit IgG.

A method has been developed for separating eosinophils from other types of leucocyte in normal individuals. Erythrocytes are sedimented with dextran, and mononuclear cells are removed on an isotonic density gradient of ficoll and sodium diatrizoate. The eosinophils and neutrophils are then washed and sedimented onto plastic petri dishes coated with human IgG and rabbit anti-human IgG antibody; As neutrophils and monocytes have Fc-binding sites for complexed rabbit IgG they attach to the dishes, and the unabsorbed normal eosinophils which lack this binding site are eluted in a purified suspension. The mean purity of the eosinophils obtained in this way was 70%, range 50-90%, and the mean yield was 49%, range 21-81%. This method provides purified eosinophils from normal people without subjecting them to osmotic or plasma membrane stimulation. Normal eosinophils which are prepared in this way are particularly suitable for studying the ways in which eosinophils became altered in disease states.

Binding Sites, Antibody↗
PubMed1976

Studies on blood eosinophils. I. Patients with a transient eosinophilia.

Studies were done on blood eosinophils from six patients with a transient eosinophilia, to see whether blood eosinophils were structurally or functionally different from blood eosinophils in eleven normal individuals. It was found that many of the patients' eosinophils were vacuolated, and some contained less specific granules than normal. These eosinophils also possessed Fc receptors for rabbit IgG. When the eosinophil counts returned to normal these abnormalities were no longer found. The nature of these alterations are discussed in relation to the properties of eosinophils in tissues and other types of phagocytic cells responding to stimulae. Suggestions are made about the mechanisms by which they could have come about. It was concluded that blood eosinophils in patients with an eosinophilia may be functionally mature or altered in response to unknown stimulae while they are in the blood.

Complement C3↗
PubMed1976

Studies on blood eosinophils. II. Patients with Löffler's cardiomyopathy.

Studies were done on blood eosinophils from four patients with raised blood eosinophil counts and heart failure. In three of the patients cardiological studies demonstrated the distinctive endocardial lesions and restrictive cardiomyopathy of Löffler's endocarditis and endomyocardial fibrosis. The fourth patient died with similar symptoms and signs. In blood films it was found that all four had more than 1 X 10(9) eosinophils per litre which were vacuolated and contained reduced numbers of crystalloid granules which were also shown to have ultrastructural changes. Unlike eosinophils from normal individuals the patients' eosinophils possessed receptors for rabbit IgG-coated erythrocytes and actively phagocytosed erythrocytes coated with rabbit IgG or human C3b. It is concluded that in these patients, a large proportion of the circulating eosinophils had developed characteristics of mature or stimulated eosinophils. This enabled them to respond to soluble substances in the bloodstream by forming endocytic vacuoles which led to degranulation of the crystalloid granules. These studies, taken in conjunction with other recent work in this field, support the concept that the restrictive cardiomyopathy of hypereosinophilic states, including Löffler's endocarditis and endomyocardial fibrosis, is a result of prolonged release of products from degranulated eosinophils while they are in the circulation.

Adult↗