A continuous-flow enzyme detector for liquid chromatography

Ultramicro enzyme assays in a capillary electrophoretic system

This paper describes an ultramicro method for achieving enzyme assays. Enzyme saturating concentrations of substrate, coenzyme when appropriate, and running buffer were mixed and used to fill a deactivated fused-silica capillary in a capillary zone electrophoresis apparatus. The enzyme glucose-6-phosphate dehydrogenase was injected by either electrophoresis or siphoning and mixed with the reagents in the capillary by electrophoretic mixing. Enzyme activity was assayed by electrophoresing the product, reduced nicotinamide adenine dinucleotide phosphate, to the detector where it was detected at 340 nm. Under constant potential, the transport velocity of enzyme and the product was generally different. This caused product to be separated from the enzyme after it was formed. Because product formation was much faster than the rate of enzyme-product separation, product accumulated. The amount of accumulated product was inversely related to operating potential. In the extreme case, the operating potential was zero. Zero potential assays were generally carried out by electrophoresing the enzyme partially through the capillary and then switching to zero potential. This capillary was left at zero potential for several minutes to allow additional product to accumulate. After this additional amplification step, potential was again applied and the product transported to the detector. Product formed under constant potential appears as a broad peak with a flat plateau. When the voltage is switched to zero at intermediate migration distance, a peak will be observed on top of this plateau. Either the eight of the plateau or the area of the peak may be used to determine enzyme concentration. The lower limit of detection was 4.6.10(-17) mol of glucose-6-phosphate dehydrogenase.

Chromatographic profiles of urinary isoenzymes in healthy children

Urinary excretion of alkaline phosphatase, gamma-glutamyltransferase and lactate dehydrogenase was studied in a carefully selected group of 155 healthy children, 83 females and 72 males. Enzyme activity was assayed in randomly collected urine samples after gel filtration of the urine specimens. On chromatograms, urinary enzymes of alkaline phosphatase, gamma-glutamyltransferase and lactate dehydrogenase were separated into 4, 2 and 5 isoenzymes, respectively. Mean values of alkaline phosphatase, gamma-glutamyltransferase and lactate dehydrogenase activity were 4.59, 21.6 and 10.0 U/g creatinine. There were no sex-related differences besides lactate dehydrogenase which showed a higher excretion in females than in males. The excretion of urinary enzymes clearly decreased with increasing age.

Automated separation and measurement of urinary isoenzymes and protein by ion-exchange liquid chromatography

This paper deals with a totally automated detection system for the assay of urinary isoenzymes and protein using high-performance liquid chromatography with a continuous post-column detection system. We attempted to determine the distribution of three enzymes in urine samples from a healthy child and in tissue extracts of rabbits. Alkaline phosphatase, gamma-glutamyltransferase and lactate dehydrogenase isoenzymes were each separated into six peaks. In comparison with the previous methods, this procedure provides better precision and accuracy, and it is sufficiently sensitive to allow the analysis without preconcentration of urine samples.

Detection of oxidized and reduced glutathione with a recycling postcolumn reaction

A rapid, sensitive, and selective method for the quantitation of both oxidized (GSSG) and reduced (GSH) glutathione in biological materials is described. Oxidized and reduced glutathione are resolved by anion-exchange high-performance liquid chromatography and detected with an in-line, recycling postcolumn reaction. The recycling reaction specifically amplifies the response to oxidized and reduced glutathione 20-100 times over that obtained with a stoichiometric reaction, permitting the detection of 2 pmol glutathione. Oxidized and reduced glutathione levels were measured in rat liver and in dog heart mitochondria. Special precautions are necessary to avoid artifacts which lead to either underestimation or overestimation of GSSG levels. GSH/GSSG ratios of approximately 100-300 were observed in samples prepared from rapidly frozen rat liver. Somewhat higher GSH/GSSG ratios were observed in isolated dog heart mitochondria.

Postcolumn detection of serum proteins with the biuret and Lowry reactions

The Lowry and biuret reactions have been adapted for the selective detection of chromatographically resolved proteins, specifically proteins separated by high-performance liquid chromatography. The protein reagents are continuously added to the column effluent and produce the characteristic chromophores with both proteins and peptides. The reaction chemistries are compatible with ion-exchange, steric exclusion, and reverse-phase chromatography. Detection limits for proteins resolved by ion-exchange are about 5 to 10 micrograms with the Lowry reaction. Peptides containing tyrosine can be detected at the 100-ng level when chromatographed on reverse-phase columns. The biuret reaction is about 8 times less sensitive for proteins and not very effective for peptides. Reaction detection can be combined with direct absorbance detection in the uv to distinguish proteinaceous peaks from other peaks containing uv-absorbing compounds.

Rapid separation and measurement of rat urinary kallikrein by high-performance liquid chromatography with a continuous flow enzyme detector

Rat urinary kallikrein was separated by high-performance liquid chromatography (HPLC) using an ion-exchange or gel-permeation column. Kallikrein activity was monitored continuously with peptidase or esterase activity using a post-reactor system directly adapted to HPLC. A PTFE helically coiled tube served as the enzyme reactor vessel. Four and three peaks with peptidase and esterase activity, respectively, were detected on application of normal rat urine.

Separation and measurement of isoenzymes and other proteins by high-performance liquid chromatography

We review the state-of-the-art of the separation of isoenzymes and other proteins by high-performance liquid chromatography (HPLC) and their subsequent, continuous detection and activity assay by post-column reaction (PCR). We describe the developments leading to current practice. These developments are categorized by column packings, post-column reaction detectors and applications in which specific analysis systems for isoenzymes, especially for lactate dehydrogenase (LD) and creatine kinase (CK) are discussed. Although HPLC coupled with PCR detection is well developed and in many cases is analytically superior to other isoenzyme technologies, it is not at the present used for routine clinical applications. We expect this trend to be reversed with clinical demonstration and the addition of commercially available automation.

Dual-detector-post-column reactor system for the detection of isoenzymes separated by high-performance liquid chromatography. I. Description and theory

We describe a dual-detector-post-column chromatographic reaction detector system that corrects for substances present in biological samples that interfere with the measurement of isoenzymes separated on a chromatographic column. The response observed at the detector in front of the reaction coil is mathematically dispersed, time transformed and subtracted from the detector behind the coil to produce a blank corrected chromatogram. The same computer program calculates peak areas and other chromatographic parameters such as height equivalent to a theoretical plate and retention time. In addition, we have evaluated the dispersion effects caused by various changes in our experimental system.

Techniques for detecting enzymes in high-performance liquid chromatography

Techniques are described for the automated detection of a series of enzymes in a high-performance liquid chromatographic system. Detection was achieved by either a direct or a coupled enzyme assay using photometric detectors. In direct detection the immediate enzymatic product was monitored. Coupled enzyme assays required additional enzyme(s) to convert the product of the primary enzyme reaction into a more easily detectable form. The efficiency of both free and immobilized coupling enzyme(s) was evaluated. The detector sensitivity could be increased three-fold by increasing the reaction temperature. This system is particularly suitable for isoenzyme profiling in biological materials.