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Biomedical subjects

R Ahmad

Publications and source records attributed to R Ahmad.

At least 145 records · Page 8Linked to original sources
PubMed1984

Reduction of lumichrome by the radical anions of CO2 and lipoamide.

The uptake of reducing equivalents of X CO-2 by lumichrome in spectrophotometric titrations has been re-examined in the light of a recently reported extinction coefficient of 10 500 M-1 cm-1 at pH 6, which is in agreement with 10 270 +/- 100 M-1 cm-1 determined here. The average uptake was 1.8 +/- 0.1, independent of pH in the range 6.3-9.0. The major product appears to be a dihydro-alloxazine, which can be reoxidized quantitatively to lumichrome by X Br-2 radicals or by O2. As in the case of dihydroflavins, oxidation by O2 is biphasic. As in the case of flavins, a two electron reduction of lumichrome was also observed with the disulphide monoanion of lipoamide (LS X 2-), but that reduction does not go to 100 per cent yield. Contrary to our earlier conclusions, which were based on an erroneous extinction coefficient, the combination of lumichrome radicals (2 X LcH----HLc--LcH) was of relatively little (less than or equal to 20 per cent) importance, and the behaviour of lumichrome on treatment with reducing species was rather similar to that of flavins.

Anions↗
PubMed1983

Reactions of lumiflavin and lumiflavin radicals with .CO2- and alcohol radicals.

The kinetics of reaction of oxidized lumiflavin (F0) with the radicals .CO2(-), CH3CHOH, and (CH3)2COH have been investigated at pH 7 and 24 +/- 1 degree C by the pulse radiolysis technique. The radicals have been shown to react with lumiflavin with second-order rate constants of 36 +/- 4, 26 +/- 3, and 20 +/- 3 in units of 10(8) M-1 s-1, respectively. These rate constants are close to the diffusion limit. The main product in each case was the lumiflavin semiquinone radical FH.. By utilization of long pulses (approximately 100 mus), it was shown that the reaction FH. + .AH(alpha) leads to FH- + A(alpha) + H+ [.AH(alpha) = .CO2(-), CH3CHOH, or (CH3)2COH] proceeded for all three types of .AH(alpha) radical with second-order rate constants of 17 (+4,-3), 9 (+5,-3), and 9 (+4,-3), respectively, in the above units. The beta-carbon radical .CH2CH(OH)CH3 added to .FH, forming an alkylated flavin, while the .CH2CH2OH radical appeared to be capable of addition or hydrogen atom donation to .FH.

Alcohols↗
PubMed1983

Human T cell proliferation in response to E. coli presented by autologous macrophages is antigen specific.

Interactions of human T cells and macrophages/monocytes (MOs) following stimulation by a Gram negative micro-organism (E. coli) have been investigated. Immunoadsorption studies showed that the E. coli-induced proliferative response of human T cells was antigen specific. The T cell pool could be selectively depleted of E. coli reactive cells by short exposure to autologous E. coli pulsed Møs. This treatment did not remove T cell reactivity directed towards an unrelated antigen (tetanus toxoid). This demonstrated the antigen specificity of the immunoadsorption step, which was further confirmed by reconstitution of E. coli reactivity after supplementing the adsorbed T cell pool with E. coli specific T cells. The Mø requirement for the E. coli-induced T cell response was confirmed and kinetic studies showed a dose-dependence with respect to the amount of E. coli used for both E. coli-induced T cell proliferation and the efficiency of immunoadsorption.

Antigens, Bacterial↗
PubMed1983

Home dialysis.

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Adolescent↗
PubMed1983

Association between rising haemoglobin concentration and renal cyst formation in patients on long term regular haemodialysis treatment.

Seventeen of 20 (85%) patients on RDT for six to 13 years were found to have acquired renal cysts. There was a significant positive association between Hb and duration of RDT. The extent of cyst was positively and significantly correlated with the latest Hb and years on dialysis. There was also a significant positive correlation between size and years on dialysis only approached statistical significance. There was no correlation between kidney size and latest Hb. Complications in patients with acquired renal cysts appear to resemble those of familial polycystic disease with the added risk of neoplasia.

Adult↗
PubMed1982

Reduction, oxidation, and addition reactions between free radicals and flavins.

Flavins and reduced flavins were reacted with a variety of free radicals produced in dilute aqueous solution at pH 7 +/- 0.1 by radiation chemical methods. The radical .CH2C(CH3)2OH and the aliphatic beta, gamma, and delta radicals of ethanol, 2-propanol, and 1-butanol added to the radical form of flavin adenine dinucleotide (FAD) (FH.) to yield products that could not be reoxidized to flavin by oxygen. The first radical also added to FAD but with a much lower efficiency. In contrast, the alpha-carbon radicals .CH(OH)CH2OH, CH3(-3) CHOH, and (CH3)2COH appeared to undergo two reactions: FH. + RR'COH leads to FH- + RR'C==O FH. + RR'COH leads to FH- + RR'C==O + H+ The formate radical anion .CO2(-) reacted similarly, producing stoichiometric two-electron reduction of riboflavin and lumiflavin as well as FAD. While eaq- also seemed capable of this, it was found to react irreversibly with FADH2, which makes it a poor reagent for producing the dihydroflavin. The dihydro form of FAD was reoxidized to FAD by the species RS. and .BR2(-). In contrast to FAD, the alloxazine lumichrome underwent only one-electron reduction and oxidation by .CO2(-) and .Br2(-), respectively.

Alcohols↗
PubMed1982

Measurement of strain rate behaviour in complete mandibular dentures.

A major cause of fracture in complete lower dentures is due to the denture falling onto a hard floor. Impact failure has never been investigated in complete dentures and in a material which is strain rate dependent, a knowledge of the maximum strain and strain rate at failure is essential if laboratory tests are to evaluate materials in a realistic manner. The work described includes brittle lacquer studies to establish the strain pattern which occurs when a denture is dropped from a height of 1 metre. This was used to orientate strain gauges and experimental dentures were then hit by a specially constructed ram driven at known velocities by a spring, whilst the strain was recorded on a storage oscilloscope. Photographs of the stored wave form were then used to establish the results at ram velocities equal to that of a denture falling 1 metre. Maximum strains were achieved of 11 x 10(3) microstrain and strain rates of 1.04 x 10(3) microstrain/ms. Laboratory impact machines for testing denture materials should therefore be designed to achieve these figures.

Dental Materials↗
PubMed1982

Plaque-forming cells in human cord blood: a soluble factor suppressing differentiation but not proliferation of B cells.

Cord blood-derived T cells have been shown to suppress differentiation of B cells into immunoglobulin-secreting cells and proliferation of mononuclear cells (MNC). We report about a soluble factor present in the supernatant of pokeweed mitogen (PWM)-stimulated cord blood MNC which was able to suppress significantly the number of plaque-forming cells (PFC) in adult MNC populations, but had no effect upon proliferation of adult MNC in response to PWM and allogeneic MNC. The number of PFC was not suppressed by supernatant from unstimulated cord blood MNC or by PWM-stimulated adult MNC.

Antibody-Producing Cells↗
PubMed1982

Functional activity of peripheral mononuclear cells in cystic fibrosis: antibodies and plaque formation.

Chronic pulmonary infection is known to constitute a major complication of cystic fibrosis (CF). In order to determine whether a defect of antibody formation is associated with this clinical finding, we have investigated antibody production on the cellular level by using a haemolytic plaque forming cell (PFC) assay. The ability of peripheral mononuclear cells (MNC) derived from patients with CF to form PFC upon stimulation by pokeweed mitogen was significantly decreased as compared to healthy control individuals (P less than 0 . 01). Levels of serum immunoglobulins of the G, A, and M classes and of sheep red blood cell agglutinating antibodies were estimated as well, but no correlation was obtained between these parameters and the number of PFC in patients with CF.

Adolescent↗
PubMed1982

Macrophage-lymphocyte interaction in response to a bacterial antigen (E. coli).

The interactions of human lymphocytes with autologous macrophages in response to a clinically relevant particulate bacterial antigen (E coli) have been investigated. Macrophages were required as accessory cells for the E coli induced activation of both T and B lymphocytes. Lymphocyte activation was assayed by determining the degree of proliferation (measured by 3H-thymidine incorporation). The proliferative response was dependent on the number of macrophages and on the amount of antigen in the culture. Macrophages briefly exposed to E. coli acquired the ability to stimulate unfractionated lymphocytes, T and B cells in the absence of free antigen. The in vitro kinetics of this reaction has been determined and analysed with respect to polyclonal B cell response and the antigen specific T cell response.

Antigens, Bacterial↗