Letter: The magnitude of intramolecular DNA optical absorbance with variation in (Na+) and GC base composition: for special application to DNA reassociation studies.
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Absorption↗
Biomedical subjects
K A Marx
Publications and source records attributed to K A Marx.
Characterization of the rapidly renaturing sequences in the main CsCl density bands of Drosophila, mouse, and human DNA.
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Animals↗
A biotinylated undecylthiophene copolymer bioconjugate for surface immobilization: creating an alkaline phosphatase chemiluminescence-based biosensor.
Methodology is described for the creation of a molecular assembly consisting of the enzyme alkaline phosphatase immobilized onto a glass surface using a biotinylated conjugated copolymer, poly(3-undecylthiophene-co-3-thiophenecarboxaldehyde) 6-biotinamidohexanohydrazone. The biotinylated polymer is attached to the inside walls of a silanized glass capillary via hydrophobic interactions, and a streptavidin-conjugated alkaline phosphatase is interfaced with the polymer through the classical biotin-streptavidin interaction. Utilizing a simple optical setup, we can detect the activity of as little as approximately 0.1 fmol of alkaline phosphatase with this molecular assembly. The assembly is mechanically robust and retains the majority of bound enzyme activity for up to 30 days. We have utilized this molecular assembly for the detection of organophosphorus-based pesticides. Both paraoxon and methyl parathion inhibit the enzyme-mediated generation of chemiluminescence signal. We are able to detect paraoxon and methyl parathion concentrations down to 500-700 ppb.
Alkaline Phosphatase↗
The quartz crystal microbalance as a continuous monitoring tool for the study of endothelial cell surface attachment and growth.
The quartz crystal microbalance (QCM) was used to monitor endothelial cell (EC) adhesion on the gold surface of an oscillating quartz crystal contained in a QCM device. A number of parameters were investigated. First, we observed differential QCM O-ring toxicities for ECs. Second, appropriate conditions for cell culture and QCM cell environment were identified that can eliminate large-scale frequency oscillations in the measurements. These artifacts are not due to added cells but originate in the time-dependent evaporation of water. Having eliminated these artifacts, we then demonstrated that the measured steady-state crystal frequency shift, Delta f, and motional resistance shift, DeltaR, were determined by the number of firmly attached ECs requiring trypsinization from the crystal surface. Last, following steady-state attachment of ECs, the EC growth stimulation by fibroblast growth factor was monitored in a continuous fashion by measuring f and R values over a 72 h. period. We observed the Delta f values to increase in a way that reflected the increase in EC number bound to the QCM surface. Following addition of ECs to the QCM, the time-dependent increase in DeltaR can be interpreted in terms of increase by the ECs of the energy dissipation properties of the solution at the solution-gold surface interface. This effect is due to their rapid surface attachment and the elaboration of their cytoskeletal properties. These results indicate that the QCM technique can be used for the study of EC attachment and growth and suggest its potential for the real time study of per unit surface area cell mass distribution dynamics and viscoelastic properties and the cells' responses to stresses or perturbations brought about using biologically active molecules.
Animals↗
Chemiluminescence-based inhibition kinetics of alkaline phosphatase in the development of a pesticide biosensor.
The use and application of the enzyme alkaline phosphatase in a chemiluminescence assay are discussed. The enzyme catalyzes the hydrolysis of a macrocyclic phosphate compound generating a chemiluminescence signal. On the basis of inhibition of this signal, a methodology for the detection and quantitation of organophosphorus-based pesticides has been developed. The methodology is studied with alkaline phosphatase in the bulk aqueous phase, and detection of the signal is accomplished by a simple optical setup. Parts per billion level detection of paraoxon and methyl parathion in bulk solutions is achieved. The technique is rapid and sensitive and is applicable to the detection of most organophosphorus-based pesticides. The results from kinetic studies indicate a mixed type of inhibition of the enzyme by paraoxon and methyl parathion. The detection methodology forms an integral part of a biosensor under development and is adaptable to incorporating optical fibers for remote detection of pesticides.
Adamantane↗
Quartz crystal microbalance measurement of self-assembled micellar tubules of the amphiphilic decyl ester of D-tyrosine and their enzymatic polymerization.
Amphiphilic decyl derivatives of D-tyrosine self-assemble into long rodlike or tubular aggregate structures in aqueous buffered solution. In this report we demonstrate the novel use of the quartz crystal microbalance (QCM) to measure the presence in solution, and subequent enzymatic polymerization, of long rodlike monomer aggregates of the decyl ester of D-tyrosine (DEDT) as a function of their formation and increasing surface binding level as pH values increase from 3 to 7. From these data, using the Sauerbray equation to calculate the effective elastic mass surface binding of deprotonated DEDT aggregates, a pKapp of 8.3 is obtained for the DEDT alpha-NH2 group protonation-deprotonation and subsequent aggregation equilibrium. Furthermore, once aggregates are bound to the QCM surface, we initiate and subsequently monitor enzymatic polymerization of the DEDT monomers by horseradish peroxidase through the measurement of significant changes in the quartz crystal frequency and motional resistance. Following the onset of polymerization, the viscoelastic properties of the bound monomer aggregates change. A final polymerized state is achieved in which the altered physical properties of the polymerized rodlike aggregates make the solution immediately above the QCM surface-solution interface behave as a Newtonian fluid, producing a nearly pure viscosity-density energy dissipative effect on the measured crystal frequency and motional resistance values.
Biotechnology↗