Search PubMed⌕ Search

Biomedical subjects

S Malik

Publications and source records attributed to S Malik.

At least 145 records · Page 8Linked to original sources
PubMed1989

Prospective study of 111 cases of thyroid surgery for post-operative morbidity and mortality.

One hundred and eleven patients were operated for various types of goitre between December, 1985 to June, 1988. These were evaluated to assess the morbidity and mortality associated with thyroid operations. A mortality of 0.9% was noted, owing to advanced age and fatal laryngeal oedema. Recurrent laryngeal nerve damage was seen in one (0.90%) case. Transient Parathyroid insufficiency appeared in 8.10% cases while the permanent damage occurred in one (0.9%) case only. Wound complications, including haematoma formation were noted in 14.40% cases. This study indicates that the thyroid surgery can be performed with acceptable morbidity and mortality, under the prevailing circumstances.

Adolescent↗
PubMed1988

Mass spectrometry studies of a novel digoxin-like substance (DLIS-2) isolated from human plasma ultrafiltrate.

Two unique low molecular weight (531) compounds with both digoxin-like immunoreactivity and Na, K-ATPase inhibitory properties have been isolated from human plasma. One of these, digoxin-like substance 2, (DLIS-2), was studied by fast atom bombardment mass spectrometry and collisionally activated dissociation mass spectrometry/mass spectrometry. The fragment patterns were interpreted as being derived from a lysophosphatidyl serine containing a novel 19:4 fatty acid side chain. The molecular formula C25H42O9NP is consistent with these observations.

Blood Proteins↗
PubMed1988

Late sigma factor of bacteriophage T4. Formation and properties of RNA polymerase-promoter complexes.

Bacteriophage T4 late gene promoters do not display sequence homology in the -35 region (Christensen, A. C., and Young, E. T. (1982) Nature 299, 369-371), suggesting an unusual geometry of RNA polymerase-promoter interaction. We have analyzed in vitro utilization of a late T4 promoter by RNA polymerase reconstituted from E. coli core enzyme (E) and bacteriophage T4 late sigma factor (sigma gp55). The E sigma gp55 holoenzyme forms a stable promoter complex which lacks protein-DNA contacts upstream from position -30 and is sensitive to direct attack by heparin. This complex is capable of reiterative oligonucleotide synthesis (abortive initiation). Kinetic analysis of complex formation reveals a rapidly forming inactive intermediate (closed complex) which is slowly isomerized into a catalytically active form (open complex). The results indicate that all components essential for promoter binding, open complex formation, and initiation of transcription are present in the "downstream" part of the RNA polymerase molecule, which is defined by the -30 to +20 footprint. On the basis of these observations and the results of others, we suggest that during transcription initiation at bipartite (Escherichia coli) promoters, an "upstream" DNA-binding domain of RNA polymerase which recognizes specific sequence elements in the -35 region plays an auxiliary role by regulating the rate of productive interactions in the downstream part of the molecule through an allosteric mechanism.

Base Sequence↗
PubMed1987

Two novel endogenous digoxin-like immunoreactive substances isolated from human plasma ultrafiltrate.

Two digoxin-like immunoreactive substances (DLIS 1 and DLIS-2) were isolated from human plasma by ultrafiltration, alkaline solvent extraction, and HPLC. Both inhibit canine Na, K-ATPase and cross-react with anti-digoxin antibodies. Their UV spectra are similar, with absorption peaks at 190 and 220 nm. FAB mass spectral analysis of both compounds yield a single dominant (M+H)+ component at m/z 532 otherwise, the fragmentation patterns are slightly different. The spectral data are consistent with the postulate that these compounds are related. Their identity as the natriuretic hormone is being investigated.

Chromatography, High Pressure Liquid↗
PubMed1987

Competition between sigma factors for core RNA polymerase.

The switch of RNA polymerase specificity from early to late promoters of bacteriophage T4 is achieved by substitution of host sigma factor, sigma 70, with the T4 induced factor, sigma gp55. However, overproduction of sigma gp55 from an expression vector is not detrimental to Escherichia coli growth. Direct competition binding assays demonstrate that sigma 70 readily displaces sigma gp55 from RNA polymerase and thereby reverses the promoter specificity of the enzyme. The displacement also occurs with the core enzyme modified by bacteriophage T4 infection. We postulate that an antagonist of sigma 70 should be formed in T4-infected cells to aid sigma gp55 in the early/late switch.

Binding, Competitive↗
PubMed1986

Chronic renal failure and cardiovascular autonomic function.

Autonomic function was assessed in 67 patients with chronic renal failure using a standardized battery of five cardiovascular reflex tests. The results showed that 38 (65%) had early or definite parasympathetic abnormalities, while 14 (24%) had additional sympathetic damage. There were no significant differences between those treated conservatively (n = 19), those on continuous ambulatory peritoneal dialysis (n = 8) and those on intermittent haemodialysis (n = 40). Cardiovascular autonomic damage is widespread among patients with chronic renal failure, however treated, and may have a number of clinical sequelae.

Adolescent↗
PubMed1986

Stationary and moving mammography grids: comparative radiation dose.

Mammography without a grid and with both a stationary and a moving grid was performed on 46 women. Mean gland dose to the breast was increased two to four times using either grid. Grid lines were apparent on films obtained with a stationary grid, but were not seen on those obtained with a moving grid. Although the radiation dose is the same with both grids, differences in the design of the two devices may lead to a personal preference in deciding which grid to use.

Female↗
PubMed1986

Light damage in the developing retina of the albino rat: an electroretinographic study.

The albino rat retina is severely damaged by exposure to bright light. The degree of damage depends upon the intensity of the exposure and its duration. In the present study, electroretinographic (ERG) responses were measured in rats exposed at different ages during the period of retinal development to 24 hr of bright light and then transferred to darkness for about 2 months. The ERG data indicated that if the bright-light exposure was done prior to 20 days of age, the retina was resistant to the light damage, and the dark-adapted ERG responses measured later were normal. In rats older than 20 days, light damage increased with age until, in rats exposed to light at age 30 days, the ERG was unrecordable. Further experiments showed that light exposure did damage the 15-day-old rat retina; however, complete recovery was attained within 15 days postexposure.

Aging↗
PubMed1985

Initiation of transcription by bacteriophage T4-modified RNA polymerase independently of host sigma factor.

After infection of Escherichia coli with bacteriophage T4 a series of modifications of RNA polymerase takes place including the association of several small polypeptides. We isolated RNA polymerase from cells abortively infected with a series of T4 mutants which arrest phage development at different stages and found that different sets of associated proteins are present in RNA polymerase in each case. The patterns of associated polypeptides seem to correlate with DNA content in the infected cells, suggesting that some of them can be involved both in DNA replication and in the transcription apparatus. One of the modified forms of RNA polymerase contains stoichiometric amounts of a protein with Mr = 25,000 (25K protein), which remains associated with the core enzyme after the removal of sigma factor by chromatography on phosphocellulose. The 25K protein was purified to homogeneity and its effect on transcription selectivity was analyzed in an in vitro system using fragments of T4 DNA as templates. The 25K protein exists in two functional forms which direct core RNA polymerase to utilize two different types of transcription start sites (class I and class II promoters). Both activities do not require host sigma factor. The two forms of 25K protein seem to compete with each other for the core enzyme. The isolated 25K protein can form stable dimers, suggesting that its two activities are associated with the dimeric and monomeric forms. Class I (but not class II) promoters can also be utilized in response to the host sigma factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiography↗
PubMed1985

Mammography using an ultrahigh-strip-density, stationary, focused grid.

A 1-mm-thick, stationary, ultrahigh-strip-density, focused grid was evaluated with respect to patient radiation dose and mammographic image quality as it affected the resolution of microcalcifications and masses. Radiographic technique was varied to determine the most useful alteration to improve image quality with the grid. Results from 89 patients demonstrated that no improvement in diagnostic ability was found in women with fatty breasts. As breast density increased, the advantage of the grid technique became more apparent. Grid mammography also often solved the problem of questionable microcalcifications with improved visualization of their number and geometry.

Breast Neoplasms↗
PubMed1984

The effect of a bacteriophage T4-induced polypeptide on host RNA polymerase interaction with promoters.

After infection of Escherichia coli with bacteriophage T4, the host RNA polymerase acquires several small phage-induced polypeptides (Stevens, A. (1974) Biochemistry 13, 493-503) and its alpha subunits get ADP-ribosylated by a virus-specific enzyme (Zillig, W., Mailhammer, R., Skorko, R., and Rohrer, H. (1977) Curr. Top. Cell. Regul. 12, 263-271). The modified polymerase displays changed enzymatic properties including sensitivity to increased salt concentration and a higher transition temperature of open promoter complex formation (promoter melting temperature). In order to assess the role of individual modifications in the changed enzyme properties, we isolated RNA polymerase from cells infected with T4 mutant defective in the ADP-ribosylating enzyme. We also purified one of the associated polypeptides, the 15,000-dalton protein which is invariably present in stoichiometric amounts in different RNA polymerase preparations. In an in vitro transcription system using T4 DNA as template, we demonstrate that the 15-kDa protein is the cause of the elevated promoter melting temperature and can induce this property when added to host RNA polymerase. We also show that the increased salt sensitivity of T4-modified polymerase is primarily the result of ADP-ribosylation of its alpha subunits.

Adenosine Diphosphate Ribose↗
PubMed1984

Changed promoter specificity and antitermination properties displayed in vitro by bacteriophage T4-modified RNA polymerase.

A 5.5 X 10(3) base-pair fragment of bacteriophage T4 DNA carrying genes 1, 3, 57, ipI and a cluster of transfer RNA genes was used as template for RNA polymerase isolated from uninfected Escherichia coli and from T4-infected bacteria. RNA transcripts were fractionated by gel electrophoresis and mapped by using as transcription template the 5.5 X 10(3) base fragment cleaved with different restriction enzymes. The comparison of the transcripts synthesized by the two RNA polymerases revealed a dramatic difference in their initiation specificities and abilities to utilize a transcription termination site. The T4-modified polymerase utilizes three new promoters on the template DNA fragment that are not utilized by the host enzyme. The modified enzyme, however, fails to produce some of the transcripts synthesized by the host RNA polymerase. The ability of T4-modified RNA polymerase to terminate transcription at a terminator present in the template DNA fragment is greatly reduced as compared to the unmodified host enzyme. The factors responsible for the new initiation and termination properties are associated with RNA polymerase core component. Analysis of RNA polymerase from bacteria infected with T4 mutants demonstrates that the new promoter specificity and the antitermination effect are caused by different factors.

DNA Restriction Enzymes↗
PubMed1984

Induction of Ca++ influx and intracellular Ca++ release in isolated rat aorta and mesenteric resistance vessels by norepinephrine activation of alpha-1 receptors.

This study was undertaken to determine which alpha adrenoceptor subtype(s) is involved in the activation of isolated rat aorta and mesenteric resistance vessels by norepinephrine and to ascertain whether norepinephrine-induced Ca++ influx into the smooth muscle is activated by one alpha adrenoceptor subtype while intracellular Ca++ release is mediated by the other subtype. The concentration-response curves for prazosin and yohimbine inhibition of norepinephrine-induced 45Ca influx, intracellular Ca++ release (as judged from contractions in Ca++-free solution) and contraction in the rat aorta indicate that the norepinephrine activation of the alpha-1 adrenoceptor was responsible for both Ca++ mobilization processes leading to norepinephrine contraction of this tissue. Contractions induced by norepinephrine in the isolated rat mesenteric resistance vessels demonstrated a phasic component, which was shown to be primarily dependent on intracellular Ca++ release, and a tonic component, which was completely dependent on Ca++ influx. Prazosin was three orders of magnitude more potent than yohimbine in inhibiting both components of the norepinephrine contracture in these vessels. We conclude that norepinephrine activation of alpha-1 adrenoceptors is responsible for both Ca++ influx and intracellular Ca++ release in isolated rat aorta and mesenteric resistance vessels.

Animals↗
PubMed1983

Studies with chlorambucil. I. Effect on lactate dehydrogenase in the testes of albino rabbits treated with multiple doses of chlorambucil.

Treatment with multiple sub-lethal doses of chlorambucil resulted in lower activity levels and specific activity of LDH and low protein content in the testes of albino rabbits. Electrophoretic analysis and assay of individual isozymes eluted from DEAE-Sephadex A-50 indicated that this loss in activity was related to the differential and/or selective action of chlorambucil on LDH4, which was affected most, while LDH3 and LDH5 were affected to a lesser degree. Kinetic inhibitory studies on purified rabbit muscle LDH in vitro revealed that chlorambucil in the reaction mixture binds to non-active enzyme sites resulting in non-competitive irreversible inhibition of LDH.

Animals↗