501
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Tan L, Muto N. Purification and reconstitution properties of human placental aromatase. A cytochrome P-450-type monooxygenase. EUROPEAN JOURNAL OF BIOCHEMISTRY 1986; 156:243-50. [PMID: 3084250 DOI: 10.1111/j.1432-1033.1986.tb09574.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The hemoprotein component of human placental aromatase (estrogen synthetase) has been purified to a high degree of homogeneity by a combination of affinity and adsorption chromatography on aminohexyl-Sepharose, concanavalin-A-Sepharose, and hydroxyapatite. The monomeric form of the enzyme has an Mr of 55000 +/- 1000 as estimated by sodium dodecyl sulfate gel electrophoresis. Its absolute spectrum shows a high-spin Soret band at 394 nm while its reduced, CO-difference spectrum has a maximum at 447 +/- 1 nm. Full reconstitution of aromatase activity was obtained when it was recombined with a homogeneous preparation of the higher-Mr form of either human placental, or bovine hepatic NADPH-cytochrome P-450 reductase. Critical factors for purification of the very unstable, membrane-bound hemoprotein with good retention of activity were, besides the chromatographic sequence, the use of the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps) during the solubilization, and the stabilizing effect of the aromatase substrate, 4-androstene-3,17-dione, throughout the procedure. In the presence of NADPH, the reconstituted enzyme system smoothly aromatizes 19-oxoandrostenedione, 19-hydroxyandrostenedione and androstenedione in this order of reactivity. The same reconstituted system also aromatized testosterone, but it was inactive towards 19-norandrostenedione. Known cytochrome P-450 inhibitors decreased its activity. We conclude: (a) the terminal oxidase of human placental aromatase is indeed a cytochrome P-450-type monooxygenase; (b) the multistep aromatization reaction of C19 androstenes is catalyzed by a single enzyme; (c) aromatization of 19-norsteroids reported by other authors must be due to a different aromatase. Experimental data obtained with the reconstituted enzyme are fully compatible with the concept of a reaction mechanism for the aromatization sequence involving an all-trans, antiparallel elimination of the 19-methyl group, the 2 beta proton and the 1 alpha proton, rather than the 1 beta proton, as generally assumed.
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502
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Chin JH, Oon CJ, Tan L, Yong YM. Treatment of irresectible hepatocellular carcinoma with intrahepatic arterial lipoidal mixed with adriamycin and mitomycin C. ANNALS OF THE ACADEMY OF MEDICINE, SINGAPORE 1986; 15:162-8. [PMID: 3019214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Four patients with advanced hepatocellular carcinoma, but with stage I functional disease, were treated with intrahepatic arterial lipoidal mixed with small doses of Adriamycin (20 mg) and Mitomycin C (10 mg). Regression was seen in 3 out of the 4 patients. In 2 patients, there was substantial regression of tumour clinically, radiologically and biochemically. The treatment was tolerable without marrow depression or deterioration of liver function. Mild fever (37 degrees C) was seen in 2 and epigastric pain in 1. This form of treatment opens up scope for further improvement in the management of irresectable hepatocellular carcinoma.
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503
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Lui P, Ng HS, Teh LB, Kwok KC, Ong YY, Tan L, Low CH, Rauff A, Seah CS. Ultrasonography in the diagnosis of cholestatic jaundice. ANNALS OF THE ACADEMY OF MEDICINE, SINGAPORE 1986; 15:182-5. [PMID: 3530104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Fifty consecutive patients (32 males and 18 females) with cholestatic jaundice were examined by grey-scale ultrasound from June 1981 to June 1983. All patients were studied without access to case notes. All patients had a diagnosis established by subsequent liver biopsy, clinical course, surgery or autopsy. Using the presence or absence of a dilated biliary system as the criterion, intrahepatic or extrahepatic cholestasis was correctly differentiated in 48 of the 50 patients, giving an overall accuracy of 96%. All 16 patients with intrahepatic cholestasis were correctly identified. Two of the 34 patients with extrahepatic cholestasis, each of whom had biliary stones, were misdiagnosed as intrahepatic cholestasis. In the 34 patients with extra-hepatic cholestasis, site of obstruction was defined in 55.9%, and specific aetiology diagnosed in 44.1%. Ultrasound proves to be an accurate method for the evaluation of cholestatic jaundice, and would have a definite value as a screening test before proceeding to invasive studies.
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504
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Chan TB, Lee KO, Rauff A, Tan L, Gwee HM. Primary hyperparathyroidism at the Singapore General Hospital. Singapore Med J 1986; 27:154-7. [PMID: 3749939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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505
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Ninan A, O'Donnell M, Hamilton K, Tan L, Sankaran K. Physiologic changes induced by endotracheal instillation and suctioning in critically ill preterm infants with and without sedation. Am J Perinatol 1986; 3:94-7. [PMID: 3964390 DOI: 10.1055/s-2007-999841] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Endotracheal instillation and subsequent suctioning produces fluctuations of intracranial pressure (ICP), mean arterial pressure (MAP), and cerebral perfusion pressure (CPP) in sick preterm infants. In an attempt to observe if these fluctuations could be minimized using sedation, we studied a group of seven sick mechanically ventilated preterm infants with and without sedation. Continuous monitoring of ICP, MAP, heart rate, CPP, and arterial oxygen tension (PaO2) were obtained. The statistical analysis of the data revealed significant blunting of fluctuations of MAP, ICP, and CPP with sedation.
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506
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Muto N, Tan L. Purification and properties of human placental NADPH-cytochrome P-450 reductase. Biochem Cell Biol 1986; 64:184-93. [PMID: 3087384 DOI: 10.1139/o86-028] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Human placental NADPH-cytochrome P-450 reductase (EC 1.6.2.4) was purified to electrophoretic homogeneity in two chromatographic steps with a high retention of bioactivity. After solubilization with 1% sodium cholate in a protective medium containing 20% glycerol, 10 microM 4-androstene-3,17-dione, 1 mM dithiothreitol, and 0.2 mM EDTA, a 35-60% ammonium sulfate precipitate was prepared. The crude protein mixture was then applied to a 2',5'-ADP-Sepharose 4B affinity column, followed by high-performance anion-exchange chromatography (Pharmacia Mono-Q column). Two forms of the reductase were isolated. One was eluted at higher salt concentration and had a relative mass (Mr) of 79 kdaltons (kDa) as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance gel permeation chromatography. A smaller size reductase with a Mr of 70 kDa, eluting at lower salt concentration, was also formed by trypsinolysis of the 79-kDa reductase. It must therefore be regarded as a proteolytic artifact. The absolute spectra in the visible region of the two reductases were identical with maxima at 376 and 452 nm, typical of a flavoprotein. They also had the same specific activity of 24.7 +/- 0.7 mumol/min per milligram protein towards cytochrome c. However, only the 79-kDa reductase showed aromatase-reconstitution activity. The homogeneity of these reductases was further confirmed by the appearance of a single peak when subjected to gradient, reversed-phase high-performance liquid chromatography. According to its amino acid composition, the 79-kDa reductase is a highly acidic and hydrophobic protein, composed of 695 residues.
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507
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508
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Sankaran K, Berscheid B, Verma V, Zakhary G, Tan L. An evaluation of total parenteral nutrition using Vamin and Aminosyn as protein base in critically ill preterm infants. JPEN J Parenter Enteral Nutr 1985; 9:439-42. [PMID: 3928917 DOI: 10.1177/0148607185009004439] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A total of 75 preterm infants with gestation less than 32 wk received total parenteral nutrition (TPN) using Vamin and Aminosyn as protein base lasting more than 20 days. They were monitored for signs of liver dysfunction, cholestatic jaundice, and TPN-induced metabolic bone disease (osteopenia of prematurity). It was observed that severity of TPN-induced cholestasis depends on the duration of TPN and quantity of protein infused. When used as a protein base, Vamin seemed to be superior to Aminosyn. TPN-induced metabolic bone disease was strongly correlated to the duration of TPN. We suggest close monitoring of critically ill preterm infants on TPN for quantity of protein infusate, liver dysfunction, cholestatic jaundice, and TPN-induced metabolic bone disease. Intravenous protein intake should be limited to less than 2.5 g/kg/day in preterm infants with gestation less than 32 wk.
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509
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Muto N, Tan L. Purification of oestrogen synthetase by high-performance liquid chromatography. Two membrane-bound enzymes from the human placenta. J Chromatogr A 1985; 326:137-46. [PMID: 3928664 DOI: 10.1016/s0021-9673(01)87439-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Human placental NADPH-cytochrome P-450 reductase, obtained by 2',5'-ADP-Sepharose affinity chromatography, was separated into two reductase-active peaks on a Pharmacia Mono-Q column. By this short, two-step chromatographic procedure, the two reductases were obtained in a homogeneous state with high retention of activity and in over 900-fold purification. Aromatase-reconstituting activity was present only in the higher-molecular-weight reductase (79 000 D), not in the smaller, 70 000 D reductase, which turned out to be a proteolysis product of the former. Both proteins were eluted as a single peak in reversed-phase high-performance liquid chromatography on a Protesil-diphenyl column. Similar results were obtained with bovine hepatic NADPH-cytochrome P-450 reductases. On the other hand, starting from a reductase-free preparation, we have obtained by high-performance ion-exchange chromatography and high-performance size-exclusion chromatography, only partial purification of the aromatase cytochrome P-450, which showed the following values: aromatase activity, 3.995 nmol/min/mg protein (60-fold purification); cytochrome P-450 content, 1.376 nmol/mg protein (23-fold purification); molecular weight, 165 000 D (estimated as an aggregate by size-exclusion chromatography). Although complete purification of the aromatase component has yet to be accomplished, our results suggest that high-performance ion-exchange chromatography on a Mono-Q column is very useful for the purification of acidic, membrane-bound enzymes with good retention of activity.
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510
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Chong PN, Cheah JS, Ng SC, Tan L, Thai AC, Rauff A, Yeo PP. Problems in the management of insulinoma. Singapore Med J 1985; 26:312-5. [PMID: 2996151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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511
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Tan L, Petit A. Inactivation of human placental aromatase by 6 alpha- and 6 beta-hydroperoxyandrostenedione. Biochem Biophys Res Commun 1985; 128:613-20. [PMID: 3994715 DOI: 10.1016/0006-291x(85)90090-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The epimeric 6 alpha- and 6 beta-hydroperoxy derivatives of androstendione caused irreversible inactivation of human placental aromatase. Microsomes from term-placentae were first preincubated in the presence of increasing concentrations of the hydroperoxides. The microsomes were then washed free of steroids and its residual aromatase activity was assayed by the tritium-exchange method to [3H]water. Aromatase activity decreased in a time-, and concentration-dependent manner; the axial, beta-hydroperoxy epimer was the slightly stronger inactivator. Less inactivation occurred when during the preincubation stage the natural aromatase substrate, androstenedione, or the anti-oxidant, dithiothreitol, was added. The sulfhydryl reagent, p-hydroxy-mercuribenzoate, decreased this protective effect. The inactivation is not dependent on the presence of NADPH. Both steroids induced a Type I difference spectrum with a Ks of 0.167 microM and 0.163 microM for the 6 alpha-, and the 6 beta-hydroperoxyandrostenedione, respectively. We suggest that these 6-hydroperoxyandrogens may function as active-site directed inhibitors and inactivators of estrogen synthetase through oxidation of cysteine residues.
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512
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Chia BL, Choo MH, Tan L, Tan A, Oon CJ, Chew PH. Two-dimensional echocardiographic abnormalities of right atrial metastatic tumors in hepatoma. Chest 1985; 87:399-401. [PMID: 2982553 DOI: 10.1378/chest.87.3.399] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
We describe two patients suffering from hepatoma who presented with right atrial metastatic tumors as a result of invasion of the inferior vena cava and extension into the right atrium. Two-dimensional echocardiographic studies detected the right atrial tumor during life in both patients and the invasion of the inferior vena cava in one patient.
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513
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Abstract
The complications arising from 195 shunting procedures are described and correlated with patient and operative variables. Neither the patient's age, sex, type of hydrocephalus, length of surgery, nor the use of prophylactic antibiotics correlated significantly with subsequent shunt complications. However, the surgeon performing the procedure and the type of shunt used were highly significant correlates.
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514
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Lopez JF, Hanson S, Orchard RC, Tan L. Quantification of mitral valvular incompetence. CATHETERIZATION AND CARDIOVASCULAR DIAGNOSIS 1985; 11:139-52. [PMID: 3886155 DOI: 10.1002/ccd.1810110205] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The hemodynamic and angiographic data of 147 individuals were analyzed in an attempt to assess the value of three techniques used in the diagnosis of mitral incompetence. One hundred patients had clinical evidence of mitral incompetence (group A) and 47 had normal hemodynamics (group B). The degree of mitral incompetence was assessed in all 147 individuals by two methods: determination of a regurgitant index (RI) using indicator dilution curves and determination of a regurgitant fraction (RF) using left ventricular volumes. In 26 patients of group A and 26 individuals in group B mitral incompetence was also assessed by cineangiocardiography. Each of these methods was compared with the clinical and hemodynamic evidence of mitral valvular incompetence. Both the determination of RI by dye dilution curves and RF by angiocardiography were found to be useful in separating normal individuals from patients with mitral valvular incompetence. Severe mitral incompetence is associated with an RI greater than 35% and with an RF greater than 55%. The degree of incompetence by either method was not well correlated with any independent hemodynamic variable. The use of cine angiocardiography to quantify the degree of mitral incompetence was found to be too subjective, depending on the observer, and thus less useful.
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515
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Chia BL, Ee B, Tan A, Choo M, Tan L. Two-dimensional and pulsed Doppler echocardiographic abnormalities in coronary artery-pulmonary artery fistula. Chest 1984; 86:901-4. [PMID: 6499554 DOI: 10.1378/chest.86.6.901] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
We describe two patients who presented with precordial continuous murmurs which were diagnosed clinically as due to patent ductus arteriosus; however, two-dimensional echocardiographic and pulsed Doppler echocardiographic studies showed dilatation of the left main coronary artery with turbulent flow during systole in the lumen in both patients. Subsequent selective coronary angiographic studies showed bilateral coronary artery-pulmonary artery fistula in one patient and left coronary artery-pulmonary artery fistula in the other. This study illustrates that in a patient presenting with a continuous murmur which is suggestive of patent ductus arteriosus, such two-dimensional and pulsed Doppler echocardiographic findings as were seen in our patients should immediately alert the physician that he may be dealing with a case of coronary arterial fistula.
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516
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Tan EC, Tung KH, Tan L, Wee A. Diverticulitis of caecum and ascending colon in Singapore. JOURNAL OF THE ROYAL COLLEGE OF SURGEONS OF EDINBURGH 1984; 29:373-6. [PMID: 6527322] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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517
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Dyck RF, Bingham W, Tan L, Rogers SL. Serum levels of C-reactive protein in neonatal respiratory distress syndrome. Clin Pediatr (Phila) 1984; 23:381-3. [PMID: 6723184 DOI: 10.1177/000992288402300703] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Serum levels of C-reactive protein (CRP) were measured within 96 hours of birth in 55 neonates with respiratory distress syndrome (RDS), 19 neonates with no significant medical illness other than an unstable cardiovascular state, and 13 neonates with a variety of pulmonary and extra-pulmonary problems either alone or in combination with RDS. The median serum CRP level in patients with RDS (2 micrograms/ml) was neither elevated nor different from CRP levels in infants with unstable cardiovascular systems (median CRP level, 2 micrograms/ml); however, neonates with other problems including pneumonia, aspiration, and extrapulmonary sepsis had significantly elevated serum CRP values (median 24 micrograms/ml). CRP levels are not elevated in neonatal RDS. Measurement of this acute phase reactant provides a rapid and reliable means of helping to distinguish infants with uncomplicated RDS from those with other serious pulmonary and extrapulmonary disease.
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518
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Goh HS, Rauff A, Foong WC, Tan L. Modified Longmire's operation for proximal extrahepatic biliary obstruction. Singapore Med J 1984; 25:92-6. [PMID: 6089354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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519
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Tan L. Visual dilation percutaneous nephrostomy tract. Urology 1984. [DOI: 10.1016/s0090-4295(84)90059-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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520
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Tan L. Visual dilation percutaneous nephrostomy tract. Urology 1984; 23:320. [PMID: 6702051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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521
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Tan L, Navennec P, Gévry G. De novo biosynthesis of 6 beta-hydroperoxyandrostenedione in human placental microsomes. Biochem Biophys Res Commun 1984; 118:805-13. [PMID: 6704107 DOI: 10.1016/0006-291x(84)91466-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Fresh human placental microsomes were incubated at 37 degrees C with a homogeneous mixture of tritium labeled 4-androstene-3,17-dione and unlabeled 6 beta-hydroperoxy-androstenedione in the presence, or absence, of various inhibitors. In all cases, radioactive 6 beta-hydroperoxyandrostenedione could be trapped in amounts significantly different from carefully conducted controls. The radioactive purity of the hydroperoxide formed was established by repetitive HPLC purifications whereby a constant ratio of radioactive counts versus peak area was obtained. The amount of tritiated 6-bèta-hydroperoxyandrostenedione produced was dependent both on the incubation time and on the microsomal protein concentration used. It was also found that in the complete absence of air, the unlabeled hydroperoxide could act as oxygen donor, supporting the formation of radioactive, 6-oxygenated metabolites. These findings are fully consistent with the concept that 6-bèta-hydroperoxyandrostenedione acts as an endogenous precursor in the formation of the corresponding 6 beta -hydroxy and 6-oxo androstene metabolites in the human placenta; a fact not previously recognized.
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522
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Sankaran K, Walton L, Tymchak Z, Hayton S, Duff E, Tan L, Best TB. Cranial volume and occipito-frontal circumference in neonates. Pediatr Res 1983; 17:949-51. [PMID: 6657325 DOI: 10.1203/00006450-198312000-00005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Occipitofrontal head circumference (OFC), using tape, and calibrated scale and cranial volumes, using styrofoam plastic cast, were measured in nine preterm and 13 term infants. Term infants had a mean +/- S.E. gestation of 40 +/- 0.2 wk and a mean +/- S.E. birth weight of 3461 +/- 108 g. Preterm infants had a mean +/- S.E. gestation of 30.5 +/- 1.4 wk and a mean +/- S.E. birth weight of 1596 +/- 211 g. Five sequential measurements were made on term infants and nine such measurements were done on preterm infants at specified time intervals. The values of cranial volume were compared with previously published results in term infants. Brain weight and cranial volumes were also compared in 10 preterm infants and seven term infants who died of non-intracranial pathology. To determine if this method is reproducible, it was tested using 50 paired measurements and was found to be within 3%. There was a significant decrease in cranial volume in term and preterm infants with time. Term infants reached the control value at 64 h of age and preterm infants reached the control value at 160 h of age. Preterm infants showed a significant decrease in OFC but term infants did not. The rate of change was not significantly different in either group.(ABSTRACT TRUNCATED AT 250 WORDS)
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523
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Tan L, Hrycay EG, Matsumoto K. Synthesis and properties of the epimeric 6-hydroperoxyandrostenediones, new substrates/inhibitors of human placental aromatase. JOURNAL OF STEROID BIOCHEMISTRY 1983; 19:1329-38. [PMID: 6621039 DOI: 10.1016/0022-4731(83)90159-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
We have recently reported the formation in bovine adrenals and in rat liver of 6 beta-hydroxy-, and 6-oxoprogesterone via the 6 beta-hydroperoxy intermediate. The presence of steroid hydroperoxides in animal tissues, however transient it may be, is not devoid of physiologic significance in view of their characteristic property as potential radical initiators. Since 6-hydroperoxides of androgens have not previously been described, we have synthesized the 2 epimeric 6 alpha-, and 6 beta-hydroperoxy-4-androstene-3,17-diones by oxygenation of 5-androstene-3,17-dione in an aprotic solvent system in the presence of dibenzoyl-peroxide. Their chemical identity and chirality were established by IR, NMR, GC-MS, and by reduction to the known 6 alpha and 6 beta-alcohols. These hydroperoxide stereoisomers could only be separated without decomposition by HPLC using a non-aqueous mobile phase. In our search for a natural, non-estrogenic inhibitor of human placental aromatase, we have studied the effect on this enzyme complex of 6 alpha- and 6 beta-OOH-androstenedione, as well as of their corresponding 6-hydroxy and 6-oxo metabolites. Aromatase activity was measured by a slightly modified version of Thompson and Siiteri's original assay based on 1 beta,2 beta-tritium exchange to 3H water. The C-6 oxygenated androgens were found to competitively inhibit the aromatase reaction in the following descending order: 6-oxo greater than 6 beta-OH greater than 6 alpha-OOH greater than 6 beta-OOH showing Ki values of resp. 2.5, 5.0, 6.5 and 7.5 microM, suggesting that they are interacting with the same active site. Moreover, both 6 alpha- and 6 beta-hydroperoxyandrostenedione are active substrates for the aromatase, giving KM values of 2.8 and 2.5 microM respectively.
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524
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Tan L. Simple, efficient ternary solvent system for the separation of luteinizing hormone-releasing hormone and enkephalins by reversed-phase high-performance liquid chromatography. J Chromatogr A 1983; 266:67-74. [PMID: 6355134 DOI: 10.1016/s0021-9673(01)90880-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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525
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Abstract
Review of 745 cases of chronic lymphocytic leukemia show that clinical staging by either the Rai or Binet method is very valuable in assessment of patients at the time of diagnosis. There is a marked decrease in survival with advancing stage (19.9 years median survival for Rai Stage 0, and 2.5 years and 2.7 years for Rai Stages 3 and 4, respectively). The definition of anemia as Hb less than 11 g/dl as in the Rai staging method appears to give slightly better discrimination among the stages than the Binet staging procedure. Patients with splenomegaly alone (Binet stage 2), however, form a small but distinct group that should be recognized. These is little to be gained by subdividing further according to size of the lymph nodes.
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526
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Tan L, Rousseau P. The chemical identity of the immunoreactive LHRH-like peptide biosynthesized in the human placenta. Biochem Biophys Res Commun 1982; 109:1061-71. [PMID: 6760865 DOI: 10.1016/0006-291x(82)92047-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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527
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Chia BL, Ee B, Tan A, Choo M, Tan L, Tan NC, Singh B, Mah EP, Quek S. The syndrome of acute mitral regurgitation -- clinical recognition, investigation and management. Singapore Med J 1982; 23:291-8. [PMID: 7167816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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528
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Tan L, Rao AJ, Yu PH. Formation of 6 beta-hydroperoxyprogesterone in rat liver microsomes. JOURNAL OF STEROID BIOCHEMISTRY 1982; 17:89-94. [PMID: 7109598 DOI: 10.1016/0022-4731(82)90597-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
To verify the concept that molecular oxygen can be enzymically introduced as such into the steroid nucleus, radioactive progesterone and also 5-pregnene-3,20-dione were incubated with microsomal preparations of rat liver. In both cases, a significant amount of radioactive 6 beta-hydroperoxyprogesterone was isolated, together with 6 beta-hydroxyprogesterone and 6-oxoprogesterone. Addition of p-hydroxymercuribenzoate and mercurichloride significantly inhibited the formation of the hydroperoxide, whereas potassium cyanide and carbon monoxide were only partially inhibitory. Addition of 6 beta-hydroperoxyprogesterone to cytochrome P-450 containing fractions of hepatic microsomes induced a Type I difference spectrum characterized by an absorption maximum at 392 nm, a minimum at 420 nm, and an isosbestic point at 407 nm. At 4 degrees C, its apparent dissociation constant was found to be in the same order of magnitude as that of 6 beta-hydroxyprogesterone, namely 1.33 microM. A new pathway in rat liver for the formation of both 6 beta-hydroxyprogesterone and 6-oxoprogesterone via the 6 beta-hydroperoxide as a common precursor, is proposed.
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529
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Chia BL, Ng R, Oh V, Ee B, Tan L. Apical hypertrophic cardiomyopathy in an Indian male. Singapore Med J 1981; 22:298-301. [PMID: 7201168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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530
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Chia BL, Tan L, Chuan TP, Ee B. The straight back syndrome. Singapore Med J 1981; 22:109-16. [PMID: 7302616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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531
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Tan L, Yu PH. De novo biosynthesis of enkephalins and their homologues in the human placenta. Biochem Biophys Res Commun 1981; 98:752-60. [PMID: 7225120 DOI: 10.1016/0006-291x(81)91176-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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532
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Tan L, Yu PH. Biosynthesis of enkephalins by chromaffin cells of bovine adrenal medulla. Biochem Biophys Res Commun 1980; 95:1901-8. [PMID: 7417348 DOI: 10.1016/s0006-291x(80)80122-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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533
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Chisholm IA, Stead S, Tan L, Melenchuk JW. Prognostic indicators in ocular hypertension. CANADIAN JOURNAL OF OPHTHALMOLOGY 1980; 15:4-8. [PMID: 7378887] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Decreased pupil size and lens opacity, rather than high intraocular pressure, have been cited as reasons for the concentric constriction of the visual field occurring in eyes with suspected glaucoma. We studied a group of eyes showing ocular hypertension and found increased concentric constriction of the visual field when compared with that of healthy control eyes. While the degree of constriction and patient age tended to predict the transition to glaucoma, we found the absence of hypermetropia to be a strong prognostic indicator.
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534
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Bowmaker GA, Tan L. The Preparation and Low-Frequency Vibrational Spectra of Some Copper(I) and Silver(I) Alkane- and Arene-monothiolate Complexes. Aust J Chem 1979. [DOI: 10.1071/ch9791443] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
A number of different
methods for preparing anionic Group 1B metal thiolate complexes have been
investigated. The compounds [Me4N] [CU2(SMe)3]
and [Et4N] [Ag5(SBut)6] are
reported for the first time, and new methods for preparing the previously known
compounds [Et4N] [Cu5(SBut)6], [Me4N]2
[CU5(SPh)7] and [Et4N]2 [Cu5(SPh)7]
are described. The far-infrared spectra of the above compounds, and of CuSMe,
CuSBut, AgSBut, [Me4N]2 [CU4(SPh)6]
and [Me4N]2 [Ag5(SPh)7] have been
obtained, and metal-sulfur stretching bands are assigned in the 150-350 cm-1
region. The low-frequency Raman spectra have also been obtained for some of
these compounds. Possible structures for the new compounds are considered in
the light of the low-frequency vibrational spectra.
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535
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Oon CJ, Yo SL, Chua D, Chio LF, Tan L, Chang CH, Chan SH. Familial primary hepatocellular carcinoma. Singapore Med J 1978; 19:218-9. [PMID: 220734] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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536
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Preiss B, Tan L, Lehoux JG. 3-Hydroxy-3-methylglutaryl coenzyme A reductase activity in beef adrenal cortex. CANADIAN JOURNAL OF BIOCHEMISTRY 1978; 56:958-62. [PMID: 31970 DOI: 10.1139/o78-149] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) activity (mevalonate:NADP+ oxidoreductase )CoA-acylating) EC 1.1.1.34) was demonstrated in beef adrenal cortex. Most of the HMG-CoA reductase activity is in the microsomal fraction while a small percentage of the activity is associated with the mitochondria, Mitochondria purified on a linear sucrose gradient are enriched in HMG-CoA reductase and cytochrome c oxidase activities. The reductase present in microsomal preparations from the whole adrenal cortex has an apparent Km of 5.6 X 10(-5) M for (R,S)-HMG-CoA. Reductase activities found in the microsomal fractions from the zona glomerulosa, the zona fasciculata, and the zona reticularis were 1.32, 7.37, and 9.74 nmol mevalonate formed per milligram protein in 30 min respectively.
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537
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Woon KY, Tan L, Tan KL. Congenital hemihypertrophy: a report of seven cases. THE JOURNAL OF THE SINGAPORE PAEDIATRIC SOCIETY 1978; 20:103-9. [PMID: 745356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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538
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Lehoux JG, Tan L, Preiss B. A comparative study of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in vertebrate adrenocortical tissues. Gen Comp Endocrinol 1977; 33:133-8. [PMID: 924108 DOI: 10.1016/0016-6480(77)90135-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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539
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Li CH, Tan L, Chung D. Isolation and primary structure of beta-endrophin and beta-lipotropin from bovine pituitary glands. Biochem Biophys Res Commun 1977; 77:1088-93. [PMID: 901511 DOI: 10.1016/s0006-291x(77)80090-9] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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540
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Yu PH, Tan L. Synthesis and properties of two new steroid hydroperoxides: an alternative pathway for the formation of 6beta-hydroxyprogesterone. JOURNAL OF STEROID BIOCHEMISTRY 1977; 8:825-34. [PMID: 563494 DOI: 10.1016/0022-4731(77)90090-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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541
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Lim CH, Tan L. Massive hepatic haemangiomatosis. Singapore Med J 1977; 18:139-43. [PMID: 929225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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542
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543
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Lim CH, Tan NC, Chia BL, Tan L. Atrial myxoma. Singapore Med J 1977; 18:68-75. [PMID: 905838] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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544
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Tan L, Rousseau J. Anaerobic degradation of the progesterone side chain: a possible new pathway for the biosynthesis of androgen hormones. Biochem Biophys Res Commun 1975; 65:1320-6. [PMID: 1052427 DOI: 10.1016/s0006-291x(75)80374-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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545
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Tan L, Falardeau P, Rousseau J. Evidence of an enzymatic 17alpha leads to 21 hydroxyl transfer in the biosynthesis of cortexolone from 17alpha-hydroperoxyprogesterone by adrenal cortex microsomes. HORMONE RESEARCH 1975; 6:213-25. [PMID: 1225813 DOI: 10.1159/000178695] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The concept of a possible biogenetic intramolecular relationship between several pairs of hydroxylated positions of corticosteroids, in particular between positions 17alpha and 21, has been proposed by us some time ago. We now present evidence that to a certain extent such a relationship can indeed exist. 18O-labelled 17alpha-hydroperoxyprogesterone was incubated under ordinary oxygen atmosphere with the microsomal fractions of bovine adrenal cortex. Following extensive purifications by thin-layer chromatography, we have isolated a metabolite with mobility characteristics corresponding to those of authentic 17,21-dihydroxy-4-pregnene-3,20-dione (cortexolone). According to its mass spectrum, this metabolite has a molecular weight of 350, i.e. 4 atomic mass units higher than the molecular weight of non-labelled cortexolone. No conversion of 17alpha-hydroperoxyprogesterone to cortexolone was observed with a previously heat-inactivated preparation. The presence of 4 additional mass units in the cortexolone metabolite means that the latter has preserved two 18O-labels in the molecule, one at position 17alpha and the other one at position 21. This can only be explained by a rearrangement reaction of the hydroperoxide group in such a way that it is accompanied by a C-17alpha to C-21 hydroxyl transfer. In the inverse case, when non-labelled 17alpha-hydroperoxyprogesterone was incubated under 99% 18O2-atmosphere, non-labelled cortexolone of molecular weight 346 was also found.
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546
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Singh D, Tan L. Pulmonary hypertension in Takayasu's arteritis. AUSTRALIAN AND NEW ZEALAND JOURNAL OF MEDICINE 1974; 4:581-5. [PMID: 4157006 DOI: 10.1111/j.1445-5994.1974.tb03242.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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547
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Dougan J, Tan L. Detection and quantitative measurement of fecal water pollution using a solid-injection gas chromatographic technique and fecal steroids as a chemical index. J Chromatogr A 1973; 86:107-16. [PMID: 4587745 DOI: 10.1016/s0021-9673(01)81239-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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548
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549
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Tan L, Wang HM, Falardeau P. 17 -Hydroperoxypregnenes. IV. A comparative study of the fragmentation by electron impact and high temperature chromatography. CANADIAN JOURNAL OF BIOCHEMISTRY 1972; 50:706-9. [PMID: 5042878 DOI: 10.1139/o72-097] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The fragmentation of 17α-hydroperoxypregnenolone and 17α-hydroperoxyprogesterone by electron impact and thermolysis is described. It is shown that the fragmentation pattern follows a common pathway for both compounds, determined exclusively by the substituents at ring-D. A new reaction in steroid chemistry, termed deoxygenation, is discovered and its mechanism explained by intramolecular hydrogen abstraction via a six-membered cyclic transition state involving the 20-ketone group.
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550
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Tan L. The role of the nurse in child care. THE NURSING JOURNAL OF SINGAPORE 1972; 12:12-3. [PMID: 4483339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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