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Biomedical subjects

M T Khan

Publications and source records attributed to M T Khan.

At least 19 recordsLinked to original sources
PubMed2004

Management of the giant-cell tumours of the distal radius.

BACKGROUND: Giant-cell tumour of the distal radius is a rare neoplasm that affects the peri-articular metaphysial region of the bone. Curettage alone or with bone grafting has been reported to be associated with high incidence of local recurrence in these tumours. In the present series, we report the results of curettage only as the treatment for primary giant-cell tumour of the distal radius carried out at a single centre. PATIENTS AND RESULTS: A total of 287 patients with giant-cell tumour have been referred to us for treatment over the last 28 years; 24 of these were found to have lesion in the distal radius. One patient underwent endoprosthetic replacement of the distal radius. The remaining 23 patients underwent curettage of the primary neoplasm. Four out of the 23 (17%) patients developed local recurrence of disease, The mean time to local recurrence was 17 months (range, 9-27 months). Complications such as collapse of the articular cartilage are more common in patients with an extensive soft tissue component of the tumour. CONCLUSIONS: Curettage alone is adequate treatment for the majority of patients with giant-cell tumours of the distal radius but some form of stabilisation may be required in the presence of extensive bone destruction.

Adolescent↗
PubMed2002

Subperiosteal schwannomas of the femur.

We report a case of two adjacent femoral subperiosteal schwannomas in a 38-year-old man. To our knowledge, this is the first report of a schwannoma arising as a surface lesion of bone. Radiographs showed focal cortical scalloping and MR imaging two small hyperintense nodules on T2-weighted and STIR images which enhanced with a gadolinium chelate.

Adult↗
PubMed2002

A comparative study of effects of cigarette and bidi smoking on respiratory function tests.

The effects of cigarette and bidi smoking on pulmonary function tests have been studied in 90 healthy males from North India Forced vital capacity (FVC), peak expiratory flow rate (PEFR), forced expiratory volume in 1 sec (FEV) were determined in 30 nonsmokers (as control group), 30 cigarette smokers and 30 bidi smokers. All the above pulmonary function parameters were found to be lower among smokers as compared to nonsmokers. Moreover, the decrease in the pulmonary function tests was greater in cigarette smokers as compared to bidi smokers.

Adult↗
PubMed2001

Characterization of membrane-associated proteasomes in WB rat liver epithelial cells.

Although proteasomes are mainly located in the cytosol, it is known that significant amounts are also associated with endoplasmic reticulum (ER) membranes where they may play a role in the degradation of specific ER membrane proteins. The present studies were undertaken to compare ER and cytosolic proteasomal activities in WB rat liver cells. N-Heptyl-beta-thioglucopyranoside (HTG) extracts of membrane or cytosol fractions were chromatographed in glycerol/ATP buffers on size-exclusion and ion-exchange columns and the elution profiles of proteasomal peptidase activity and immunoreactive components of the 20S complex, 19S complex, and PA28 were compared. Cytosol fractions showed a single peak of chymotrypsin-like peptidase activity (Cht-L), which was inhibited completely by 5 microM lactacystin (LC) or SDS (0.03%) and corresponded to 26S proteasomes based upon the presence of both 20S and 19S components. By comparison, membrane fractions contained two major peaks of Cht-L activity. The first peak shared the same properties as the peak activity observed in cytosol fractions. However, the second peak was stimulated by SDS and was LC-insensitive (5 microM) and contained trypsin-like (T-L) and peptide-glutamyl peptidase (PGPH) but no cathepsin or calcium-activated protease activities. PA28 activator protein was present in both membrane and cytosol fractions. Thus, the principal difference between cytosolic and membrane activity was that the latter fractions contained a novel membrane-associated LC-insensitive protease(s) catalyzing three of the major peptidase activities of the proteasome.

Acetylcysteine↗
PubMed2001

The effects of aqueous extracts of Desmodium gangeticum DC. (Leguminosae) on the central nervous system.

The aqueous extract of Desmodium gangeticum DC. (Leguminosae) showed no analgesic activity in the hot plate method, but it showed severe anti-writhing activity in the acetic acid-induced abdominal writhing assay. It exhibited moderate central nervous system depressant activity in the spontaneous motor activity, hole cross, and open field tests and hole board tests. The effects of this extract on locomotion were compared with some standard CNS drugs.

Analgesics, Opioid↗
PubMed2000

Structure and function of procollagen C-proteinase (mTolloid) domains determined by protease digestion, circular dichroism, binding to procollagen type I, and computer modeling.

Procollagen C-proteinase-2 (pCP-2, mTld) is derived from the longest splicing variant of the gene encoding bone morphogenetic protein 1 (BMP-1). The variants have identical amino terminal signal peptides, prodomains and astacin-like protease domains. However, they differ in the length of their carboxy terminal part, which in pCP-2 has the composition CUB1, CUB2, EGF-like1, CUB3, EGF-like2, CUB4, CUB5, and C-tail. In the shorter form, pCP-1 (i.e., BMP-1), the sequence ends after the CUB3-domain. Using a combination of mutagenesis and structural approaches, we have investigated the structure and function of subfragments of pCP-2. The full-length latent recombinant enzyme and its N-terminally truncated form lacking the prodomain were tested for their enzymic activity. The intact protein showed only partial processing of procollagen type I, whereas the truncated form expressed enzymic activity indistinguishable from its native counterpart purified from chick embryo tendons. These results clearly demonstrated that the prodomain is required for the latency of the enzyme but not for its correct folding. Limited proteolysis of the recombinant protein with alpha-chymotrypsin produced four discrete fragments revealing the location of cleavage sites between the repetitive CUB/EGF domains. The results provide evidence that the CUB sequences form independently folded modules that are stabilized by two pairs of internal disulfide bridges. The modules are linked to each other by more flexible, hinge-like peptides. Solid-phase binding assays with isolated CUB domains and immobilized procollagen type I demonstrated that the first three but not the last two CUB domains specifically bound to the substrate. To define putative sites for CUB-CUB or CUB-substrate interactions, we generated molecular models for pCP-2 CUB domains. The models were obtained using as a template the structure of CUB domain in zona pellucida adhesion protein PSP-I/PSP-II from porcine sperm. The predicted conformations for homology models were, subsequently, confirmed by circular dichroism spectroscopy of polypeptide domains isolated following limited proteolysis with alpha-chymotrypsin.

Amino Acid Sequence↗
PubMed2000

High tibial osteotomy without internal fixation for medial unicompartmental osteoarthrosis.

Between 1982 and 1993, a total of 35 patients underwent high tibial osteotomy for medial unicompartmental osteoarthrosis. The osteotomy was performed high in the tibia without the use of jigs, and internal fixation devices were avoided. Patients were assessed using the British Association for Surgery of the Knee score, and satisfactory results with minimal complications were obtained. Our results indicate that in a select group of patients, high tibial osteotomy preserves bone stock and is performed near the deformity so that excellent correction is achieved and recurrence of varus deformity is avoided.

Adult↗
PubMed1998

Allograft bone transplantation: a Sheffield experience.

There has been an increase in demand for allograft bone in recent years. This type of bone provides an excellent material to fill in bony defects, but could be associated with an incidence of infection. Any newly established tissue bank has to meet the very stringent criteria to process and store bone and maintain a donor and recipient database to avoid transmission of infection. The Sheffield Tissue Bank has been functioning since 1989 and until 1993 has provided bone allografts to 220 patients; these have been used mainly to reconstruct defects at revision hip and knee arthroplasty and for scoliosis surgery. There have been no cases of disease transmission and the rate of infection has been reduced by strict screening protocols. This paper outlines our experience, problems and success with human bone banking.

Adolescent↗
PubMed1997

Identification and characterization of a calmodulin-binding domain in Ral-A, a Ras-related GTP-binding protein purified from human erythrocyte membrane.

A 28-kDa protein (p28) has been purified from Triton X-100 extracts of human erythrocyte plasma membrane by calmodulin affinity chromatography. Based on internal peptide sequencing and its protein amino acid composition, this protein has been shown to be highly related, if not identical to, Ral-A, a Ras-related GTP-binding protein. This protein assignment is consistent with the findings that p28 binds [32P]GTP specifically and has low GTPase activity. In this study we describe the identification and characterization of a calmodulin-binding domain in Ral-A. The Ca2+-dependent interaction of p28 with calmodulin was first detected by a calmodulin affinity column. Gel overlay experiments of both p28 and recombinant Ral-A with biotinylated calmodulin provided strong evidence that Ral-A is a calmodulin-binding protein. A peptide of 18 residues (P18) with the sequence SKEKNGKKKRKSLAKRIR has been identified as a putative calmodulin-binding domain in Ral-A, because it comprises a basic/hydrophobic composition with the propensity to form an amphiphilic helix. P18 was synthesized, and its interaction with calmodulin by gel overlay was shown to be Ca2+-dependent. Circular dichroism analysis demonstrated that this interaction results in less alpha-helical content upon calmodulin complex formation. These results indicate that Ral-A is a calmodulin-binding protein, raising the possibility that it may be associated with Ca2+-dependent intracellular signaling pathways.

Amino Acid Sequence↗
PubMed1996

The podiatric treatment of hallux abducto valgus and its associated condition, bunion, with Tagetes patula.

To assess the effectiveness of marigold therapy using Tagetes patula preparations, a double-blind placebo-controlled trial was designed to be carried out over a period of eight weeks. Sixty patients were entered in the trial. Twenty patients with bilateral hallux abducto valgus and its associated condition, bunion, were randomly selected from 37 subjects for group A. For group B, 40 patients with unilateral hallux abducto valgus and bunion were randomly selected from 69 subjects and subdivided into groups Ba and Bb. Patients with ulcerated conditions, those on medication and those who had undergone surgery for the condition were excluded. The results obtained were highly significant (P < 0.001), suggesting that T. patula preparations, plus protective pad, were effective in reducing the width of the lesion and level of pain of hallux abducto valgus.

Hallux Valgus↗
PubMed1995

Identification and purification of a 90-kDa membrane-bound endogenous inhibitor of multicatalytic proteinase from human erythrocytes.

We have identified and purified an endogenous inhibitor of multicatalytic proteinase (MCP) from human erythrocyte membranes. The inhibitor showed a molecular mass of 90 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The inhibitor protein was purified from the erythrocyte membranes using Heparinagarose and hydroxylapatite chromatography and the size exclusion on a Biogel A 1.5 m column in the presence of high salt. The 90-kDa protein inhibited all three peptidase activities of MCP; trypsin-like, chymotrypsin-like and peptidyl glutamyl peptide hydrolyzing (PGPH). However, it failed to cause any significant inhibition of caseinolytic activity of MCP, suggesting that the regulation of proteinase and peptidase activities is distinct. The inhibition of the chymotrypsin-like activity was noncompetitive. The results suggest that the 90-kDa inhibitor protein may be an important regulator of membrane-bound MCP.

Amino Acid Sequence↗
PubMed1995

Unlike its human counterpart, band 3 anion exchange protein from goat erythrocyte membrane shows a lack of reactivity against various -SH oxidants and protease treatments.

Studies involving a number of -SH oxidants and proteases were made to analyse the organization of band 3 in goat erythrocyte membrane. -SH oxidizing agents such as diamide, Cu2+.o-phenanthroline and phenylene dimaleimide, known to cause cross-linking of human erythrocyte band 3, failed to show any cross-linking in the case of goat band 3 protein. When resolved to their individual components using -SH reducing agent beta-mercaptoethanol, high molecular weight protein adducts formed as a result of diamide treatment did not show any band 3 on two-dimensional electrophoresis. Also no proteolysis of band 3 was detected when intact goat erythrocytes were exposed to pronase, though marked proteolysis was noticed in the case of human band 3 proteins under similar conditions. These studies involving -SH oxidant and protease treatments suggest a different organization for goat erythrocyte band 3 protein as compared to that of human in erythrocyte membrane.

Animals↗
PubMed1995

Studies on the differential morphological alterations in human and goat erythrocytes against ATP depletion and Ca(2+)-induced stresses.

Erythrocyte membranes obtained from goat exhibited Ca2+/calmodulin-insensitive (Ca(2+)-Mg2+)-ATPase activity and the activity levels were significantly lower as compared to those obtained from human erythrocyte membranes. Although Ca2+/ionophore A23187 -treatment enhanced the intracellular Ca2+ levels in both the freshly collected human and goat erythrocytes, negligible loss of ATP was noticed in goat erythrocytes under such conditions. Also, fluoride, a known metabolic inhibitor, caused a lesser ATP depletion in goat erythrocytes compared to that of human. Goat erythrocytes showed remarkable rigidity to shape change and unlike human erythrocytes, did not undergo echinocytic formation as a result of metabolic depletion and Ca2+/ionophore A23187-treatments. These studies suggest the participation of (Ca(2+)-Mg2+)-ATPase -independent mechanism(s) for Ca(2+)-extrusion.

Adenosine Triphosphate↗
PubMed1994

Membrane-bound high molecular mass proteinases from human erythrocytes.

Two high molecular mass proteinases, multicatalytic proteinase (MCP) and a new high molecular mass proteinase (HMP) with only chymotrypsin-like activity (Khan et al. (1994) J. Biol. Chem. 269, 10016-10021) from human erythrocyte membranes, have been compared. For this purpose, MCP was purified from human erythrocyte membranes in the active form towards synthetic peptide substrates; it also hydrolysed the protein substrates [14]methyl casein and [14C]oxidised insulin beta chain at 37 degrees C. MCP from plasma membranes exhibited hollow cylindrical structures also typical of cytosolic forms. Radiolabelled diisopropyl fluorophosphate, [3H]DFP, a serine proteinase inhibitor, labelled a band of Mr 23 000 in membrane MCP. By contrast, no labelling was obtained with HMP. Chymotrypsin-like activity of HMP was also found to be insensitive to DFP. On the other hand, DFP inhibited chymotrypsin-like and peptidylglutamyl peptide hydrolysing activities of membrane MCP, with no effect on its trypsin-like activity. The inhibition of MCP by DFP was concentration-dependent. These studies showed that MCP and HMP represent two distinct kinds of proteinases with chymotrypsin-like activities and can be distinguished by the serine proteinase inhibitor DFP.

Amino Acid Sequence↗
PubMed1994

Characterization of a novel high molecular mass protein with peptidase activity purified from the human erythrocyte membrane by calmodulin affinity chromatography.

A previously undescribed high molecular mass protein (HMP) from human erythrocyte membranes was solubilized by Triton X-100 and purified on a calmodulin-agarose column in the presence of Ca2+. It was shown to have a native molecular mass of 522-560 kDa, comprised of a single subunit of a molecular mass of 28 kDa (p28). The protein is associated with the lipid bilayer rather than with the cytoskeletal component of the membrane. The purified HMP showed peptidase-hydrolyzing activity toward substrates containing hydrophobic amino acids at the P1 position of the P2-P1 cleavage site. The activity was inhibited by serine proteinase inhibitors (leupeptin, phenylmethansulfonyl fluoride) and chymotrypsin inhibitors in particular (chymostatin, N-tosyl-L-phenylalanine chloromethyl ketone). The enzyme exhibited maximal activity at slightly alkaline pH (7.5-8.5) and at 37 degrees C and was stimulated over a narrow range of SDS concentrations (maximal at 0.05%). HMP was found to cross-react in Western blots with an antibody raised against the rabbit multicatalytic proteinase. The single subunit of HMP therefore contains both the catalytic activity and a sequence necessary for its association into a multimeric complex. The properties of the human erythrocyte membrane HMP described indicate that it is a novel peptidase related to the ubiquitous multicatalytic proteinase.

Amino Acid Sequence↗