Biomedical subjects
Publications and source records attributed to J Klimek.
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Cytosolic malic enzyme (L-malate: NADP oxidoreductase decarboxylating, EC I. I. I.40) has been isolated and purified from postmitochondrial supernatant of human term placenta by ammonium sulphate fractionation, chromatography on diethylaminoethyl- (DEAE-)cellulose, Sepharose 6B, ADP-Sepharose 4B and Ultrogel AcA-34 to apparent homogeneity as judged from polyacrylamide gel electrophoresis (PAGE). The specific activity of the purified enzyme was 24.0 mumol X min-1 X mg-1 protein, which corresponds to about 7500-fold purification. The molecular weight of the native enzyme was determined by gel filtration to be about 250,000. Sodium dodecyl sulphate- (SDS-)PAGE showed one polypeptide band of molecular weight 63,000. It appears that the native protein is a tetramer composed of subunits of identical molecular weight. The isoelectric point of the purified malic enzyme was pH 5.55. The enzyme was shown to carboxylate pyruvate in the presence of high concentrations of pyruvate and bicarbonate at about 80 per cent of the rate of the forward reaction. The optimum pH for the carboxylation reaction was pH 7.3, and that for the decarboxylation reaction varied with malate concentration. The Km values, determined at pH 7.2, for malate, NADP+, Mn2+, and Mg2+ were 81 microM, 10 microM, 2.5 microM and 0.6 mM, respectively. The Km values for pyruvate, NADPH and bicarbonate were 4 mM, 25 microM and 20 mM, respectively. The enzyme converted malate to pyruvate (at pH 6.3) in the presence of 5 mM NAD+ at approximately 80 per cent of the maximum rate with NADP+. It exhibited oxaloacetate decarboxylase activity at about 10 per cent of the rate of oxidative decarboxylation of malate (with NADP+ as coenzyme) and pyruvate reductase activity at about 4 per cent of the rate of oxidative decarboxylation of malate with NADP+. The oxidative decarboxylation of malate was inhibited by malate at lower values of pH of incubation medium. This inhibition gradually decreased as the pH of the incubation medium increased. No inhibition was observed at pH 8.2. The addition of purified cytoplasmic malic enzyme, pyruvate, bicarbonate and NADPH generating system (consisting of NADP+, glucose 6-phosphate, glucose 6-phosphate dehydrogenase) stimulated about twofold progesterone biosynthesis by the isolated human placental mitochondria. This stimulation was abolished by arsenite and fluorocitrate. A possible role for the cytosolic malic enzyme in the regulation of progesterone biosynthesis in human placenta is discussed.
The aim of the present study was to evaluate the effect of fluoride on the progression of erosive demineralisation in human enamel and dentine using a cyclic de- and remineralisation model in vitro. The mineral content expressed in micrometres was determined daily by longitudinal microradiography (LMR) and presented as cumulative mineral loss over 5 days. For erosive demineralisation, all samples were immersed in 0.05 M citric acid (pH 2.3) for 6x10 min/day and stored in a remineralisation solution. Fluoridation measures were performed as follows: group 1: control, no fluoridation; group 2: toothpaste fluoridation 3x5 min/daily (NaF, 0.15% F-); group 3: toothpaste fluoridation as group 2 and additionally application of a fluoride mouthrinse (Olaflur/SnF2, 0.025%F-) 3x5 min/daily and on days 1 and 3 gel fluoridation (Olaflur/NaF; 1.25% F-) for 1x5 min. After the first experimental day, no significant differences were found between the groups. However, after 5 days the erosive mineral loss values for enamel were 147.5+/-18.7 microm in the control group, 128.1+/-15.0 microm in group 2 (p< or =0.05) and 116.1+/-12.4 microm in group 3 (p< or =0.001). In dentine, the respective values were 136.7+/-16.4, 111.8+/-26.9 (p< or =0.001) and 60.3+/-17.8 (p< or =0.001). The intensive fluoridation significantly reduced erosion progression in enamel but had a more pronounced effect on dentine. The results suggest that subjects with erosive lesions should use an intensive fluoridation measure.
The aim of the present study was to evaluate the effects of fluoride on erosive mineral loss in human enamel and dentine using a cyclic de- and remineralisation model in situ. The study was a three-treatment (5 days each) crossover design involving 4 (enamel) or 6 (dentine) healthy volunteers. Samples were recessed in palatal mouth appliances and worn day and night except during meals and were demineralised extraorally with 0.05 M citric acid (pH 2.3) for 6 x 5 min daily. Fluoridation was performed with toothpaste (SnF2/Olaflur; 0.14% F-) for 3 x 5 min daily (toothpaste fluoridation) or with toothpaste in combination with a mouthrinse (SnF2/Olaflur; 0.025% F-) for 3 x 5 min daily and with a gel (NaF/Olaflur, 1.25% F-) on days 1 and 3 instead of the toothpaste (intensive fluoridation). In the control group no fluoridation was performed. Mineral loss (microm) was determined with the use of longitudinal microradiography. In enamel, mineral loss was 40.7 +/- 15.1 microm in the control group, 18.3 +/- 12.4 microm after toothpaste fluoridation and 5.0 +/- 12.2 microm after intensive fluoridation. The respective values for dentine were 49.0 +/- 15.4, 35.0 +/- 15.5 and 19.8 +/- 12.0 microm. All differences were statistically significant (p < or = 0.001). The results indicate that intensive fluoridation is effective in preventing enamel and dentine from mineral loss even under severely erosive conditions.
The study is a comparison of methods for the quantitative measurement of erosive mineral loss including longitudinal microradiography (LMR), profilometry (PM), and analysis of calcium (CA) and phosphorus (PA) in the erosion solution. Polished human enamel samples were taped, covered with nail varnish and the edges of the resulting enamel window marked with drilled holes as a reference. All samples were subjected to baseline LMR. Sixty samples each were eroded with citric acid (0.05 M; pH 2.3; 10 ml per sample) for 30, 60, 90, or 120 min. Erosive loss of each sample was estimated by the four methods. All methods revealed a linear erosive loss over time and showed good linear correlation. Values calculated from PM and LMR were both approximately 20% lower than those from CA and PA. After 30 min erosion, LMR showed no significant correlation with the other three methods. With LMR, erosive loss below 20 microm should be interpreted with care.
This study evaluated occlusal margins and surfaces of composite and ceramic inlays after finishing and polishing in vivo. Eighty Class II cavities surrounded by enamel were prepared by two experienced dentists. Forty cavities were restored with indirect microhybrid composite inlays (Tetric), the balance were treated with heat-pressed glass ceramic inlays (IPS Empress). Using a rubber dam, the inlays were inserted adhesively with a dual curing composite of high viscosity (Variolink Ultra). Finishing was performed with the sequence of a 30 microm and 20 microm diamond (finishing method FM 1) or a 30 microm diamond followed by a tungsten carbide finishing bur (FM 2). The composite inlays were divided into four groups of 10 that were finished and polished according to the following protocol: (A) FM 2/Diafix-oral, (B) FM 2/MPS gel, (C) FM 1/Diafix-oral, (D) FM 1/MPS gel. Ten ceramic inlays each were treated as follows: (E) FM 2/MPS gel, (F) FM 1/MPS gel, (G) FM 2/ Diamond polisher, (H) FM 1/Ceramiste silicon polishers. After polishing, replicas of the restorations were fabricated. The replicas were examined by SEM with respect to margin quality (portion of continuous margins, overhangs, submargination and marginal imperfections). Furthermore, surface properties were evaluated qualitatively, which included assessing roundness of the contours in three grades (smooth rounding, few edged contours or predominantly edged contours) and evaluation of the surface roughness (smooth and homogeneous surface, minor roughness or severe roughness). Quantitative analysis of the occlusal composite and ceramic inlay margins showed that 52.2%-84.6% were rated as continuous, 0%-14.0% were characterized by overhangs and 0.7%-10.8% by submargination. A portion of 4.9%-18.1% margins revealed imperfections. The amount of marginal gap formation was negligible. Composite and ceramic inlays showed a similar behavior with respect to marginal quality after finishing and polishing. Overall, there were no significant differences among the four methods applied to composite and the four methods used on ceramic inlays with respect to margin quality. The use of a 30 microm diamond followed by a tungsten carbide bur on composite and ceramic inlays resulted in a significantly larger portion of continuous margins compared to finishing with two diamonds (p=0.049). Qualitative evaluation of composite and ceramic inlays revealed that 50%-80% of the occlusal surfaces were characterized by few edged contours and 10%-50% by smooth rounding. With respect to roughness, smooth surfaces prevailed both on composite (67.5%-80.0%) and ceramic inlays (64.5%-77.3%). Overall, no significant differences were detectable between the methods for finishing and polishing composite inlays and the methods applied to ceramic restorations with respect to roundness of contours and surface roughness.
PURPOSE: Hyperhomocysteinemia is considered an independent risk factor for atherosclerosis and thrombosis. The purpose of this study was to evaluate plasma homocysteine, red blood cell folate, plasma folate, and plasma vitamin B12 concentration in patients with exudative age-related macular degeneration (ARMD). METHODS: The participants of this study included 30 patients aged 60 to 71 years (mean age 66.2+/-3.6) with exudative ARMD. Plasma homocysteine levels were determined by high performance liquid chromatography (HPLC). Red blood cell folate, plasma folate, and plasma vitamin B12 concentration were determined using a standard kit (Dualcount Solid Phase No Boill radioassay kit for B12/folic acid, DPC Diagnostic, USA) by radioassay method. RESULTS: The plasma concentration of Hcy (14.88+/-6.23 micromol/L) in ARMD patients was significantly increased (p<0.0001) compared with the control group (8.72+/-3.34 micromol/L). We found not a significant decrease of the plasma vitamin B12 concentration in the ARMD group (476.88+/-220.91 pg/mL) compared with the control group (527.08+/-208.97 pg/mL). Red blood cell folate (158.44+/-56.30 ng/mL) and plasma folate (6.5+/-3.4 ng/mL) in ARMD patients were also not significantly decreased when compared with the control group (183.86+/-59.33 ng/mL and 7.93+/-5.05 ng/mL). CONCLUSIONS: Hyperhomocysteinemia might be one of the risk factors for the exudative form of ARMD.