Comparison of mechanical and chemomechanical methods of caries removal in deciduous and permanent teeth: a SEM study.

BACKGROUND: Mechanical method of caries removal is associated with the removal of sound tooth structure, production of pain, heat, annoying sounds, and vibrations. Chemomechanical caries removal method is based on removal of only carious dentin leaving sound dentin intact. AIM: The aim of this study was to compare the efficacy of mechanical and chemomechanical methods of caries removal in deciduous and permanent teeth. STUDY DESIGN: A total of 30 carious teeth including 15 deciduous and 15 permanent teeth having dentinal caries selected randomly and cut into two halves through center of the lesion, were subjected to caries removal by mechanical (Group A), and chemomechanical methods (Group B). Time taken for removal of caries was noted with stopwatch. Samples were prepared and seen under the scanning electron microscope for the presence of bacterial colonies. Data were analyzed using statistical package for social sciences (SPSS) Software. RESULTS: No significant difference was found for the presence of bacterial colonies in both groups of deciduous and permanent teeth; however, time taken for caries removal by the chemomechanical method was twice than the mechanical method. CONCLUSION: despite the insignificant presence of bacterial colonies and twice time taken as compared to mechanical method, chemomechanical method was easy to introduce, was painless, did not form smear layer and conserved the sound tooth structure.

Kinetic interactions of glycine with substrates and effectors of phosphenolpyruvate carboxylase from maize leaves.

Glycine enhanced the sensitivity of maize phosphenolpyruvate carboxylase to the activator glucose 6-phosphate and reduced the sensitivity of the enzyme to the inhibitors malate and aspartate. The effects of glycine on the kinetic constants for these other effectors were greater than its effect on the Km for substrate, raising the Ki(malate) 11-fold and reducing Ka(glucose6-P) 7-fold, while reducing the Km(PEP) by 3-fold. Kinetically saturating levels of glycine and glucose 6-phosphate acted synergistically to raise Ki(malate) higher than that observed with either activator alone. Glycine and glucose 6-phosphate also synergistically reduced aspartate inhibition. Dual inhibitor analysis indicated that aspartate and malate bind in a mutually exclusive manner, and thus probably compete for the same inhibitor site. In contrast, the synergism between glycine and glucose 6-phosphate indicate that these activators bind at separate sites. Glycine also reduced the Km(Mg) by 3-fold but had no significant effect on the Km of bicarbonate.

Metabolite activation of crassulacean Acid metabolism and c(4) phosphoenolpyruvate carboxylase.

The effects of glycine, alanine, serine, and various phosphorylated metabolites on the activity of phosphoenolpyruvate (PEP) carboxylase from Zea mays and Crassula argentea were studied. The maize enzyme was found to be activated by amino acids at a site that is separate from the glucose 6-phosphate binding site. The combination of glycine and glucose 6-phosphate synergistically reduced the apparent K(m) of the enzyme for PEP and increased the apparent V(max). Of the amino acids tested, glycine showed the lowest apparent K(a) and caused the greatest activation. d-Isomers of alanine and serine were more effective activators than the l-isomers. Unlike the maize enzyme, the Crassula enzyme was not activated by amino acids. Activation of either the Crassula or maize enzyme by glucose 6-phosphate occurred without dephosphorylation of the activator molecule. Furthermore, the Crassula enzyme was activated by two compounds containing phosphonate groups whose carbon-phosphorus bonds were not cleaved by the enzyme. A study of analogs of glucose 6-phosphate with Crassula PEP carboxylase revealed that the identity of the ring heteroatom was a significant structural feature affecting activation. Activation was not highly sensitive to the orientation of the hydroxyl group at the second or fourth carbon positions or to the presence of a hydroxyl group at the second position. However, the position of the phosphate group was found to be a significant factor.

Effect of Diethylpyrocarbonate on the Allosteric Properties of Phosphoenolpyruvate Carboxylase from Crassula argentea.

Phosphoenolpyruvate carboxylase from the Crassulacean acid metabolism plant Crassula argentea was substantially desensitized to the effects of regulatory ligands by treatment with diethylpyrocarbonate, a reagent which selectively modifies histidyl residues. Desensitization of the enzyme to the inhibitor malate and the activator glucose 6-phosphate was accompanied by the appearance of a peak in the ultraviolet difference spectrum at 240 nanometers, indicating the formation of ethoxyformylhistidyl derivatives. Hydroxylamine reversed part of the spectral change under native conditions, and almost all of the change under denaturing conditions, but failed to restore sensitivity to effectors. The pH profiles of desensitization to malate and glucose 6-phosphate indicated the involvement of groups on the enzyme with pK, values of 6.8 and 6.4, respectively. Under denaturing conditions, a total of 15 histidine residues per subunit were modified by diethylpyrocarbonate, whereas for the native enzyme nine histidines were modified per subunit. Effector desensitization occurs after the modification of two to three histidyl residues per subunit. The presence of malate reduced the apparent rate constant for desensitization by 60%, suggesting that the modification occurred at the malate binding site. Diethylpyrocarbonate treatment also eliminated the kinetic lag caused by malate. Glucose 6-phosphate did not protect the enzyme against diethylpyrocarbonate-induced desensitization.

Malate-Induced Hysteresis of Phosphoenolpyruvate Carboxylase from Crassula argentea.

The hysteretic behavior of phosphoenolpyruvate (PEP) carboxylase from Crassula argentea has been investigated. Incubation of the purified enzyme with the inhibitor malate prior to starting the reaction by the addition of PEP resulted in a kinetic lag of several minutes duration. The length of the lag was inversely proportional to the enzyme concentration, suggesting subunit association-dissociation as the hysteretic mechanism, rather than a mechanism based on a slow conformational change in the enzyme. Dynamic laser light scattering measurements also support this conclusion, showing that the diffusion coefficient of malate-incubated enzyme slowly decreased after the reaction was started by the addition of PEP. Lags were observed only at pH values of 7.5 or lower. Maximum lags were observed after 10 min of preincubation with malate. Fumarate and succinate, which like malate caused mixed inhibition, also caused lags. In contrast, no lag was induced by malate in the presence of PEP or by the competitive inhibitor phosphoglycolate. The activators glucose 6-phosphate and malonate decreased the malate-induced lag.

Metal Ion Interactions with Phosphoenolpyruvate Carboxylase from Crassula argentea and Zea mays.

Metal ion interactions with phosphoenolpyruvate carboxylase from the CAM plant Crassula argentea and the C(4) plant Zea mays were kinetically analyzed. Fe(2+) and Cd(2+) were found to be active metal cofactors along with the previously known active metals Mg(2+), Mn(2+), and Co(2+). In studies with the Crassula enzyme, Mg(2+) yielded the highest V(max) value but also generated the highest values of K(m) ((metal)) and K(m) ((pep)). For these five active metals lower K(m) ((metal)) values tended to be associated with lower K(m) ((pep)) values. PEP saturation curves showed more kinetic cooperativity than the corresponding metal saturation curves. The activating metal ions all have ionic radii in the range of 0.86 to 1.09 A. Ca(2+), Sr(2+), Ba(2+), and Ni(2+) inhibited competitively with respect to Mg(2+), whereas Be(2+), Cu(2+), Zn(2+), and Pd(2+) showed mixed-type inhibition. V(max) trends with the five active metals were similar for the C. argentea and Z. mays enzymes except that Cd(2+) was less effective with the maize enzyme. K(m) ((metal)) values were 10- to 60-fold higher in the enzyme from Z. mays.

Modulation of the activity of NAD malic enzyme from solanum tuberosum by changes in oligomeric state.

The effects of pH, NaCl, and malate2- on the equilibrium between dimeric and higher-molecular-weight forms of NAD malic enzyme from Solanum tuberosum var. Chieftain have been analyzed by monitoring the kinetic changes associated with disaggregation [S. D. Grover and R. T. Wedding (1982) Plant Physiol. 70, 1169-1172]. At pH values above 7.0 the enzyme was disaggregated to the dimeric, high-Km(malate) form by preincubation with NaCl, with a half-maximal effect at 25 mM. At low pH the enzyme remained in the low-Km(malate) (tetramer or octamer) form. Malate protected against disaggregation to the high-Km form in preincubation, and this effect was half-maximal at 6 mM. At pH 7.3, in the absence of malate, half-maximal disaggregation occurred at 580 nM enzyme. Varying the enzyme concentration in the assay led to kinetic changes which fit equations based on an associating enzyme model [B. I. Kurganov (1967) Mol. Biol. (Moscow) 1, 17-27]. This analysis confirmed that the dimer has intrinsic activity, with Vm somewhat lower than that of the tetramer but a Km(malate) that was 9-fold higher than that of the tetramer. Malate decreased the Kd for disaggregation of the enzyme during assay approximately 20-fold, with a half-maximal effect at 3 to 4 mM. In contrast, high NaCl concentrations in the assay increased the Kd for disaggregation in a manner which was competitive with the effect of malate on Kd. The physiological significance of these aggregation state changes is discussed.

Kinetic Ramifications of the Association-Dissociation Behavior of NAD Malic Enzyme : A Possible Regulatory Mechanism.

NAD malic enzyme can exist in dimer, tetramer, or octamer form. Freshly prepared enzyme from Solanum tuberosum var. Chieftan exists predominantly as the octamer and during storage is progressively converted into lower molecular weight forms. High ionic strength favors dimer formation, whereas high concentrations of malate or citrate favor tetramer formation. The tetramer is the most active form, having a low K(m) for malate and a high V(max). The dimer, with its high K(m) and low V(max), is the least active form. Malate may regulate NAD malic enzyme by controlling its state of oligomerization.

Disulfiram inhibition of the alternative respiratory pathway in plant mitochondria.

Disulfiram (tetraethylthiuram disulfide) was found to be a potent and selective inhibitor of the alternative respiratory path of plant mitochondria. The onset of inhibition by disulfiram takes several minutes and the inhibition is not readily reversed by washing, nor by metal ions. By contrast, thiols such as dithiothreitol not only reverse, but also prevent, disulfiram inhibition. Inhibition by disulfiram and by hydroxamic acids are not mutually exclusive. Structural analogs of disulfiram are far less potent inhibitors, with the exception of bisethyl xanthogen. Inhibition is due to disulfiram, per se, and not to its reduction product, diethyldithiocarbamate, a powerful chelator. Accordingly, the inhibitory effect of disulfiram is considered to involve the formation of mixed disulfides with one or more sulfhydryl groups in the alternative path. Disulfiram does not act as an electron sink diverting electron flow from oxygen.Disulfiram inhibition was observed only with isolated mitochondria or submitochondrial particles. In intact cells or tissues either a failure to absorb disulfiram, or its dissipation in the cytosol, precludes inhibition. In vitro, bovine serum albumin reduces disulfiram inhibition by complexing free inhibitor.The binding of (35)S-disulfiram by cyanide-resistant mitochondria displays the same kinetics as disulfiram inhibition. A comparison was made of (35)S-disulfiram binding by cyanide-sensitive and cyanide-resistant potato mitochondria. Cyanide-resistant mitochondria were obtained from ethylene-treated potato tubers. Incorporation of label proved essentially the same in both types of mitochondria, suggesting that the disulfiram-sensitive component of the alternative path is present in untreated potato tubers, and is not induced by ethylene.