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Biomedical subjects

S Khalid

Publications and source records attributed to S Khalid.

11 recordsLinked to original sources
PubMed2006

Can WHO therapy failure criteria for non-severe pneumonia be improved in children aged 2-59 months?

SETTING: In the recent past, there have been reports of rising treatment failure rates for non-severe pneumonia. It is felt that World Health Organization (WHO) criteria for therapy failure are too sensitive and that many children are unnecessarily classified as failures. We studied alternative, less sensitive therapy failure criteria. METHODS: In this nested study we followed the clinical course of non-severe pneumonia in children aged 2-59 months using alternative therapy failure criteria. All children received amoxicillin and were followed up on days 3, 5 and 14 after enrollment. On day 3, children were labelled as therapy failure only if their condition had deteriorated. These failure rates were compared with those using WHO definitions. RESULTS: During the study period, 876 children with non-severe pneumonia were followed up until day 14. On day 3, using alternative therapy failure criteria, 31 (3.5%) children were labelled as therapy failure compared to 95 (10.8%) using current WHO criteria. The difference was statistically significant (P = 0.001). CONCLUSIONS: The alternative therapy failure criteria work reasonably well, without causing any higher risk to children with non-severe pneumonia. Antibiotics should be changed only in those children who show signs of deterioration on day 3. This would prevent unnecessary changes in antibiotic treatment in many children.

Acute Disease↗
PubMed2004

Frequency of hereditary thrombophilia: an AKUH experience.

OBJECTIVE: To determine the frequency of various causes of hereditary thrombophilia at a referral laboratory and the age and gender distribution. METHODS: This is a descriptive study incorporating a retrospective analysis of requests for thrombophilia screening sent to Clinical laboratory, Aga Khan University Hospital from November 1995 to May 2002. Patients were screened for hereditary causes of thrombophilia including Protein C, Protein S, antithrombin III, Factor V Leiden and homocysteine. Frequency of each disorder; and age and sex distribution was determined. RESULTS: All the patients suspected clinically for thrombophilia were screened. Of the 2825 patients, 70 were diagnosed to have inheritance as a cause of thrombophilia with a frequency of 2.3% for protein C deficiency, 1.4% for protein S deficiency, 1.5% for antithrombin III deficiency, 14.2% for factor V leiden mutation and 2.0% for homocystenemia. CONCLUSION: All the causes of hereditary thrombophilia can be diagnosed by relatively simple laboratory methods, however because of the low frequency of these disorders the screening of general population is not indicated in the absence of clinical symptoms. More prospective studies are required to define the occurrence of these disorders and other causes of thrombosis.

Adolescent↗
PubMed2001

Theoretical study of Mn K-edge in La1-xCaxMnO3.

Effects of (i) local magnetic ordering, (ii) lattice distortions, and (iii) Mn 3d - O 2p hybridization on the shape of Mn K- edge XANES spectra of La1-xCa(x)MnO3 have been evaluated numerically and compared with available experimental data. We calculated the spin-polarized Mn K-edge spectra. An energy splitting between spin-up and spin-down XANES of 0.5-1.1 eV contributes to the broadening of the total XANES below T(N)(T(C)). To simulate lattice polaronic distortions across a MI transition the Mn K-edge spectra were calculated twice: assuming R-3c (R=1.96 A) and Pbnm (R1=1.91, R2=1.97, and R1=2.16 A) symmetries. Results could qualitatively reproduce the observed energy "shift" across the transition. A pre-edge peak at E approximately 6542 eV and feature B3 at approximately 6 eV above the main peak were found to be related to the Mn 3d - O 2p hybridization. The feature B3 should be assigned to a shake-up transition. The calculated K-edge spectrum was obtained as a convolution product of the single-electron XANES and the spectrum of many-body excitations in the Mn-O electronic states in the presence of the 1s core-hole.

Journal Article↗
PubMed2000

Multiple infection, recombination and genome relationships among begomovirus isolates found in cotton and other plants in Pakistan.

Begomoviruses occur in many plant species in Pakistan and are associated with an epidemic of cotton leaf curl disease that has developed since 1985. PCR analysis with primer pairs specific for each of four already sequenced types of DNA-A of cotton leaf curl virus (CLCuV-PK types a, 26, 72b and 804a), or for okra yellow vein mosaic virus (OYVMV), indicated that many individual naturally infected plants of cotton and other malvaceous species contained two or three begomovirus sequences. Similarly, sequence differences among overlapping fragments of begomovirus DNA-A, amplified from individual naturally infected plants, indicated much multiple infection in malvaceous and non-malvaceous species. Some cotton plants contained DNA-A sequences typical of begomoviruses from non-malvaceous species, and some non-malvaceous plants contained sequences typical of CLCuV-PK. Some DNA-A sequences were chimaeric; they each included elements typical of different types of CLCuV-PK, or of different malvaceous and/or non-malvaceous begomoviruses. Often an apparent recombination site occurred at the origin of replication. No complete CLCuV-PK DNA-A sequence was found in malvaceous or non-malvaceous species collected in Pakistan outside the area of the cotton leaf curl epidemic but chimaeric sequences, including a part that was typical of CLCuV-PK DNA-A, did occur there. We suggest that recombination among such pre-existing sequences was crucial for the emergence of CLCuV-PK. Recombination, following multiple infection, could also explain the network of relationships among many of the begomoviruses found in the Indian subcontinent, and their evolutionary divergence, as a group, from begomoviruses causing similar diseases in other geographical regions.

Base Sequence↗
PubMed1993

An extended X-ray absorption fine structure investigation of the structure of the active site of lactoperoxidase.

Native lactoperoxidase, compound III, and the reduced forms (at pH 6 and 9) were studied using X-ray absorption spectroscopy (XAS). Native lactoperoxidase has four pyrrole nitrogen ligands at an average distance of 2.04 +/- 0.01 A, a proximal ligand at 1.91 +/- 0.02 A, and a sixth (distal) ligand at 2.16 +/- 0.03 A. Lactoperoxidase native enzyme has a first coordination shell structure that is similar to that of native lignin peroxidase [Sinclair, R., Yamazaki, I., Bumpus, J., Brock, B., Chang, C.-S., Albo, A., & Powers, L. (1992) Biochemistry 31, 4892-4900] and different from that of horseradish peroxidase [Chance, B., Powers, L., Ching, Y., Poulos, T., Schonbaum, G., Yamazaki, I., & Paul, K. (1984) Arch. Biochem. Biophys. 235, 596-611]. Similarly, lactoperoxidase compound III resembles lignin peroxidase compound III. The five-coordinated ferrous form was stable at pH 9, but at pH 6 it was rapidly converted to the six-coordinated form with a distal ligand at 2.18 +/- 0.03 A. No evidence typical of changes in spin state was obtained at the different pH values.

Absorptiometry, Photon↗
PubMed1993

pH dependence of the active site of horseradish peroxidase compound II.

Using X-ray absorption spectroscopy, we investigated the active site of horseradish peroxidase (HRP) compound II at two different pH values. The results indicate that the bond length of the sixth coordinated ligand of the active site was 1.90 +/- 0.02 A at pH 7, decreasing to 1.72 +/- 0.02 A at pH 10. The average iron-to-pyrrole nitrogen and the proximal ligand bond lengths showed no significant changes. The position of higher coordination shells around the iron center changed, implying that some movement or deformation of nearby amino acid residues and/or of the heme occurred. Results of this study suggest that the decrease of the Fe-O bond length of HRP compound II at the higher pH might be attributed to the loss of a hydrogen bond which is present between the oxygen ligand and an amino acid residue in the heme pocket at pH 7.

Absorptiometry, Photon↗
PubMed1989

Extended X-ray absorption fine structure study of Rhodospirillum rubrum and Rhodospirillum molischianum cytochromes c': relationship between heme stereochemistry and spin state.

An EXAFS study on the oxidized and reduced forms of cytochromes c' from Rhodospirillum rubrum and Rhodospirillum molischianum was performed at pH 7. The cytochromes c' have an apparent coordination number of 5 in both oxidation states. Average Fe-ligand bond lengths of 2.02 +/- 0.025 and 2.06 +/- 0.025 A are obtained in their oxidized and reduced forms, respectively. By use of suitable values for the Fe-NHis bond length and Fe out-of-plane displacement, as determined by small molecule crystallographic techniques, the Fe-Npyrrole bond lengths and the porphyrin center-to-Npyrrole distance have been estimated for cytochrome c' in both of its oxidation states. With this model, estimates of the Fe-Npyrrole bond lengths are 2.01 +/- 0.03 and 2.05 +/- 0.03 A, for the oxidized and reduced cytochromes c', respectively. The center-to-Npyrrole distance is estimated to be 1.99 +/- 0.03 A for oxidized cytochrome c' and 2.03 +/- 0.03 A for reduced cytochrome c'.

Cytochrome c Group↗
PubMed1987

Kinetic, structural, and spectroscopic identification of geminate states of myoglobin: a ligand binding site on the reaction pathway.

Elementary steps or geminate states in the reaction of gaseous ligands with transport proteins delineate the trajectory of the ligand and its rebinding to the heme. By use of kinetic studies of the 765-nm optical "conformation" band, three geminate states were identified for temperatures less than approximately 100 K. MbCO, which is accumulated by photolysis between 1.2 and approximately 10 K, was characterized by our previous optical and X-ray absorption studies [Chance, B., Fischetti, R., & Powers, L. (1983) Biochemistry 22, 3820-3829]. Between 10 and approximately 100 K, geminate states that are also identified that have recombination rates of approximately 10(3) s-1 and approximately 10(-5) s-1 (40 K). Thus, it is possible to maintain a steady-state nearly homogeneous population of the slowest recombining geminate state, Mb, by regulated continuous illumination (optical pumping). Both X-ray absorption and resonance Raman studies under similar conditions of optical pumping show that the heme structure around the iron in Mb is similar to that of MbCO. In both geminate states, the iron-proximal histidine distance remains unchanged (+/- 0.02 A) from that of MbCO while the iron to pyrrole nitrogen average distance has not fully relaxed to that of the deoxy state. In MbCO the CO remains close to iron but not bound, and the Fe...CO angle, which is bent in MbCO (127 +/- 4 degrees C), is decreased by approximately 15 degrees [Powers, L., Sessler, J. L., Woolery, G. L., & Chance, B. (1984) Biochemistry 23, 5519-5523]. The CO molecule in Mb, however, has moved approximately 0.7 A further from iron. Computer graphics modeling of the crystal structure of MbCO places the CO in a crevice in the heme pocket that is just large enough for the CO molecule end-on. Above approximately 100 K resonance Raman studies show that this structure relaxes to the deoxy state.

Binding Sites↗
PubMed1984

Antimalarial psychosis revisited.

Drug-induced psychosis resulted from the administration of quinacrine hydrochloride at a dosage of 100 mg twice daily for the treatment of discoid lupus. After two weeks of drug treatment, the patient exhibited symptoms similar to those seen in the manic phase of bipolar affective disorder. Although the incidence of antimalarial psychosis is unclear and perhaps small, we recommend close observation of patients for behavioral changes suggesting the development of antimalarial psychosis. Astute observation, leading to the early detection of behavioral changes, may help avert the development of a costly and disabling complication of drug therapy.

Female↗