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Biomedical subjects

S Merchant

Publications and source records attributed to S Merchant.

At least 37 records · Page 2Linked to original sources
PubMed1987

Metal ion regulated gene expression: use of a plastocyanin-less mutant of Chlamydomonas reinhardtii to study the Cu(II)-dependent expression of cytochrome c-552.

Ac-208, a plastocyanin-deficient strain of Chlamydomonas reinhardtii, lacks the mRNA for pre-apoplastocyanin although Southern analyses indicate no gross deletion in the single gene for pre-apoplastocyanin. The alternative electron carrier, cytochrome c-552, is expressed only in Cu(II)-deficient cells of the mutant. Thus, the mutant strain can grow photoautotrophically in Cu(II)-deficient but not in Cu(II)-sufficient medium. This indicates that the absence of plastocyanin is the only defect (with respect to photosynthesis) in ac-208. Phenotypic revertants of ac-208 are capable of photoautotrophic growth by virtue of constitutive [with respect to Cu(II)] synthesis of cytochrome c-552. The revertant phenotype is attributed to a decreased internal concentration of Cu(II). This indicates that the Cu(II)-dependent expression of cytochrome c-552 synthesis is affected directly by the concentration of Cu(II) rather than indirectly by the level of plastocyanin in the cell.

Chlamydomonas↗
PubMed1986

Rapid degradation of apoplastocyanin in Cu(II)-deficient cells of Chlamydomonas reinhardtii.

Although plastocyanin is not detected in Cu(II)-deficient cells of Chlamydomonas reinhardtii, accumulation of messenger RNA for pre-apoplastocyanin is independent of the concentration of Cu(II) in the medium (Merchant, S., and Bogorad, L. (1986) Mol. Cell. Biol. 6, 462-469). This work shows that the synthesis, transport, and processing of pre-apoplastocyanin also appear to be unaffected in cells grown in Cu(II)-deficient medium. However, the mature protein, presumably formed after import of the precursor into the chloroplast, is rapidly degraded in Cu(II)-deficient cells. The half-life of the mature protein is estimated to be between 16 and 18 min in cells grown in Cu(II)-deficient medium. In cells grown in medium containing Cu(II), the mature protein is stable. The proteolytic activity thus appears to be specific for apoplastocyanin versus plastocyanin and thereby accounts for the absence of accumulated plastocyanin in Cu(II)-deficient cells. This process may be part of a general mechanism designed to remove chloroplast proteins which cannot be utilized.

Apoproteins↗
PubMed1986

Regulation by copper of the expression of plastocyanin and cytochrome c552 in Chlamydomonas reinhardi.

Plastocyanin and cytochrome c552 are interchangeable electron carriers in the photosynthetic electron transfer chains of some cyanobacteria and green algae (P. M. Wood, Eur. J. Biochem. 87:9-19, 1978; G. Sandmann et al., Arch. Microbiol. 134:23-27, 1983). Chlamydomonas reinhardi cells respond to the availability of copper in the medium and accordingly accumulate either plastocyanin (if copper is available) or cytochrome c552 (if copper is not available). The response occurs in both heterotrophically and phototrophically grown cells. We have studied the molecular level at which this response occurs. No immunoreactive polypeptide is detectable under conditions where the mature protein is not spectroscopically detectable. Both plastocyanin and cytochrome c552 appear to be translated (in vitro) from polyadenylated mRNA as precursors of higher molecular weight. RNA was isolated from cells grown either under conditions favorable for the accumulation of plastocyanin (medium with Cu2+) or for the accumulation of cytochrome c552 (without Cu2+ added to the medium). Translatable mRNA for preapoplastocyanin was detected in both RNA preparations, although mature plastocyanin was detected in C. reinhardi cells only when copper was added to the culture. Translatable mRNA for preapocytochrome, on the other hand, was detected only in cells grown under conditions where cytochrome c552 accumulates (i.e., in the absence of copper). We conclude that copper-mediated regulation of plastocyanin and cytochrome c552 accumulation is effected at different levels, the former at the level of stable protein and the latter at the level of stable mRNA.

Chlamydomonas↗
PubMed1984

Short term variability in FEV1: relation to pretest activity, level of FEV1, and smoking habits.

The natural variability in forced expiratory volume in one second (FEV1) over 20 minutes was determined in 54 fit hospital employees and 13 patients with restrictive lung disorders. Initial FEV1 ranged from 1.1 to 6.3 1 BTPS. Variability when expressed as absolute change was similar at all levels of FEV1, so that, when expressed as percentage change, variability decreased with increasing FEV1. Smoking habits did not appear to affect variability but activity before the test did. On the basis of these results an absolute change in FEV1 of 190 ml would be necessary for 95% confidence that the change in FEV1 occurred other than by chance in any one individual. This suggests that the absolute change in FEV1 might be a more reliable criterion than percentage change when distinguishing between natural variability and a response to inhalation of bronchodilators.

Adolescent↗
PubMed1983

Identification of the alpha and beta subunits of the chloroplast coupling factor one in Chlamydomonas reinhardi.

The alpha and beta subunits of the Chlamydomonas reinhardi coupling factor one have been identified by an immunochemical method and by the reaction of dicyclohexylcarbodiimide with the beta subunit. Antibodies raised against the C. reinhardi subunit with the highest apparent molecular weight react with the alpha subunit of spinach coupling factor one and antibodies raised against the beta subunit of the spinach chloroplast enzyme cross-react with the C. reinhardi subunit of lower apparent molecular weight. Dicyclohexylcarbodiimide also reacts with this subunit. We conclude therefore that the two subunits of highest apparent molecular weight can be named alpha and beta in order of decreasing apparent molecular weight, in contrast to the nomenclature suggested by Piccioni, R. G., Bennoun, P. and Chua, N.-H. [(1981) Eur. J. Biochem. 117, 93-102].

Chlamydomonas↗
PubMed1983

Molecular weight and subunit stoichiometry of the chloroplast coupling factor 1 from Chlamydomonas reinhardi.

The molecular weight of the Chlamydomonas reinhardi coupling factor 1 (CF1) is 4.2 X 10(5) as determined by gel exclusion chromatography and sedimentation equilibrium. In addition, a measured sedimentation coefficient of 12.9 S results in a calculated molecular weight of 3.9 X 10(5). These molecular weight estimates are too high to support an alpha 2 beta 2-type subunit stoichiometry and are suggestive of an alpha 3 beta 3-type enzyme. The subunit stoichiometry of the C. reinhardi CF1 was determined from the distribution of label into the subunits of uniformly labeled CF1. An alpha: beta: gamma: epsilon ration of 2.9:2.9:1:1 was obtained.

Chlamydomonas↗
PubMed1981

Isolation, purification, and characterization of coupling factor 1 from Chlamydomonas reinhardi.

Chloroplast thylakoid particles were prepared from wild-type Chlamydomonas reinhardi by gentle sonication. These particles catalyzed phenazine methosulfate dependent photophosphorylation with rates ranging from 300 to 700 mumol of adenosine 5'-triphosphate (ATP) formed (mg of chlorophyll)-1h-1. Photophosphorylation was not sensitive to tentoxin but was sensitive to an anticoupling factor 1 (CF1) antiserum preparation made against spinach CF1. The C. reinhardi chloroplast CF1 was isolated from thylakoid particles by either chloroform or ethylenediaminetraacetic acid extraction. The former enzyme appeared to be missing the gamma subunit and did not reconstitute with partially resolved thylakoid particles. The latter enzyme reconstituted with partially resolved particles and had a specific activity at 37 degrees C of 2-5 umol of ATP hydrolyzed (mg of protein)-1 min-1. The enzyme utilized both MnATP and MgATP. CaATP was a poor substrate, and SrATP was not hydrolyzed. The enzyme was not activated by heat or proteolysis but was stimulated approximately 2-fold by 50 mM dithiothreitol. Alcohols reversibly stimulated the ATPase activity of the enzyme 5-25-fold. Ethanol, 20%, dramatically lowered the temperature optimum from approximately 75 to approximately 45 degrees C and slightly lowered the pH optimum from 8.5 to 8.2. Ethanol had no effect on the activation energy of the ATPase reaction (17 +/- 1.7 kcal/mol). The kinetics of the ATPase reaction catalyzed by the C. reinhardi enzyme are complex. Both free divalent cations and divalent cation ATP inhibited the activity of the enzyme. The apparent Km for MgTAP (55 uM free Mg2+) was approximately 0.2 mM.

Adenosine Triphosphatases↗
PubMed1981

Developmental defects of the lungs.

Poor lung development was first noted on scintigraphy using 99mTc-phytate in 32 children. They had all been referred for a hepatosplenic scan but the initial circulatory phase of the radiopharmaceutical was also recorded as a routine procedure. In 3 patients it revealed aplasia of an entire lung; bilateral pulmonary hypoplasia was observed in 14 of 16 patients with diaphragmatic herniae. Six patients with congenital heart enlargement showed a poorly developed ipsilateral lung; 5 of 6 patients with dextrocardia without an intracardiac defect had a larger left lung compared with the right lung; both pulmonary beds appeared equal in a patient with mesocardia.

Adolescent↗
PubMed1980

Failure of propranolol and metoprolol to alter ventilatory responses to carbon dioxide and exercise.

Neither propranolol (80 mg) nor metoprolol (100 mg) give orally to eight normal subjects altered mean ventilatory responses to carbon dioxide or to moderate graded exercise. Incremental doses of the drugs to totals of 320 mg propranolol and 400 mg metoprolol also did not effect these ventilatory responses. Both drugs markedly decreased the heart rate response to exercise. Neither propranolol nor metoprolol are likely to cause CO2 retention by an effect on the ventilatory responses to inhaled carbon dioxide or to exercise.

Adult↗
PubMed1979

A radiocolloid study of the reticulo-endothelial system in tropical diseases.

Radiocolloids were used to study the trapping function of the reticulo-endothelial system in 361 children with infectious or non-infectious tropical diseases. Responses of the system varied not only between different types of diseases but also between individuals suffering from the same type of disease, as illustrated (primarily) by numerous scans of the liver and spleen.

Child↗
PubMed1978

The effect of aerosol ipratropium bromide and salbutamol on exercise tolerance in chronic bronchitis.

In a double-blind placebo controlled trial in 24 patients fulfilling the MRC criteria for chronic bronchitis, ipratropium bromide 40 microgram and salbutamol 200 microgram produced similar and significant (P less than 0.001) increases in forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). A greater increase in FEV1 and FVC was seen when both drugs were used together, but this increase did not differ significantly from that produced by either drug alone. Salbutamol increased 12-minute walking distance significantly (P less than 0.001) by 62 +/- 15 metres, whereas the increase of 43 +/- 15 metres observed after ipratropium was not significant (P less than 0.05). With both drugs in combination 12-minute walking distance increased by 72 +/- 15 metres, but this change was not significantly different from that observed with salbutamol alone. If aerosol bronchodilators in the doses used in this study are to be given with a view to improving exercise tolerance in such patients than salbutamol would appear to be the aerosol of choice.

Aerosols↗
PubMed1977

Frequency of inferior vena caval abnormalcy due to a juxtaposed pathology.

Radionuclide inferior vena cavagrams were done in 135 patients who had hepatomegaly, splenomegaly or a mass in the vicinity of the inferior vena cava (I.V.C.). 2-5mCi 66mTc phytate, 99mTc S colloid, 99mTc O4-, 99mTc-LIDA, 99mTc pyridoxyledene glutamate or 113mIn colloid were injected directly and rapidly into either a malleolar or a femoral vein while the patient lay supine under the 13.5'' detector head of a scinticamera. Rapid sequential scintiphotos were manually taken at approximately 1 sec. interval for 20-30 sec. Thus iliac vein, I.V.C., cardiopulmonary zone in infants, aorta and the arterial phase were visualized. 48% of these subjects had an abnormal I.V.C. and the depictions were interestingly varied, indicating that different patients responded in a different manner even to grossly similar pathologies. It became evident that this soft walled vessel could be compressed by both fluids and neoplastic tissue (Fig. 1, 2); the long I.V.C. channel could also be segmentally pushed away by a mass in its vicinity. (Fig. 2, 3, 4). An abnormal arterial flush usually differentiated between benign (Fig. 2) and malignant (Fig. 3) lesions, even when the mass was extra-hepatic (Fig. 4) and retiroperitoneal (Fig. 5). Such a systematic study of I.V.C. had not been possible earlier since the classical x-ray contrast inferior vena cavagram necessitates venous dissection, passage of a catheter, and the injection of large volume of fluid under an unphysiologically high pressure. The simplified radionuclide technique, however, permitted the study of neonates and critically ill subjects with massive ascites, while retaining a satisfactory reproducability.

Abdominal Muscles↗
PubMed1976

Radiorespirometric study of carbohydrate metabolism in childhood liver disease.

The need for a suitable parameter to evaluate patients with chronic liver disease has been felt for some time, especially in order to judge the response to surgical shunts and the influence of certain drugs and diets on the liver. Since the liver is a major organ for carbohydrate metabolism, it was decided to analyze the in vivo oxidation of such substrates as glucose and galactose labeled with 14C. Moderately advanced "Indian childhood cirrhosis" and idiopathic fatty hepatic infiltration were selected to represent diffuse chronic liver disease. Oral administration of 14C-U-glucose or 14C-1-galactose was followed by analyses of 14CO2 in breath by liquid scintillation counting. Conversion of 14C-glucose to 14CO2 was accelerated by both diseases. On the other hand, oxidation of 14C-galactose was slowed in fatty infiltration and was markedly subnormal in Indian childhood cirrhosis.

Carbon Dioxide↗