Analytical aspects of immobilized enzyme columns

LETTER TO THE EDITOR

An isocyanurate silane coupling agent effectively attaches to E-glass fibers both from aqueous or CCl4 solution. SEM revealed remarkably different glass surface topographies that were solvent dependent. Application of the coupling agent from CCl4 solution gave rise to unprecendented polymeric bridges between adjacent parallel fibers. The existence of such large bridging structures has only recently been postulated, and it was not thought that such theoretical projections would ever be observed, as polymeric bridging structures typically should collapse in the absence of solvent. Copyright 1997 Academic Press. Copyright 1997Academic Press

Surface modification of the biomedical polymer poly(ethylene terephthalate)

X-ray photoelectron spectroscopy was used to characterize modified surfaces of a biomedically important polymer, poly(ethylene terephthalate). Several modification schemes were investigated and direct silanization with 3-aminopropyltriethoxysilane was found to be the optimum procedure, resulting in an aminated surface. Surface coverage of up to 100% was achieved with retention of the polymeric structural integrity. Further activation of the silanized surface was accomplished with two cross-linkers, glutaraldehyde and sebacoyl chloride. A simple biomolecule, L-cysteine, was successfully immobilized onto a surface pre-treated with 3-aminopropyltriethoxysilane and glutaraldehyde, with a coverage of 42%.

A synthetic functional metabolic compartment. The role of propinquity in a linked pair of immobilized enzymes

A system was created to model the influence of microcompartments on linked enzymatic reactions. Creatine kinase and hexokinase were covalently attached to Sepharose beads. The gel could be perfused in a specially constructed chamber inside a 360-MHz NMR spectrometer at different flow rates with solutions containing various concentrations of substrates. 31P NMR studies were carried out on the linked enzymatic reaction, creatine phosphate + glucose----creatine + glucose 6-phosphate in two enzyme gels differing in only one aspect, the average distance between hexokinase and creatine kinase. At a distance on the order of 0.1 mm between the enzymes, the average bulk concentrations of substrates and products in the perfusate determined the overall function of the linked system. At an average distance of the order of 10 nm, flux through the linked pair was much higher and much less dependent on the concentration of the intermediate substrate/product ADP/ATP. Even at adenine nucleotide concentrations far below the Km of hexokinase, substantial amounts of glucose 6-phosphate were produced when the enzymes were near but not when they were distant. From saturation transfer measurements and turnover calculations, the lifetime of ATP in the system is estimated to be 0.14-0.5 s when the enzymes are near. This compares to 6 s for distant enzymes. From this it appears that the pair of linked enzymes comprise a functional compartment supported by propinquity in which hexokinase has preferential access to ATP produced by creatine kinase, and creatine kinase to ADP from the hexokinase reaction.