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Biomedical subjects

B Zak

Publications and source records attributed to B Zak.

At least 19 recordsLinked to original sources
PubMed1991

Fluorometric determination of phosphatidylcholine as a measure of phospholipid methylation.

The successive methylation of phosphatidylethanolamine to phosphatidylcholine (phospholipid methylation) has been measured by the incorporation of S-[methyl-3H]adenosylmethionine or colorimetric assay of phosphatidylcholine extracted from adipocyte plasma membranes. A fluorometric assay for phosphatidylcholine was developed to measure phospholipid methylation. This assay is 10 times more sensitive than the colorimetric assay and demonstrates no significant interference with other methylated phospholipids. The fluorometric assay was used to determine a biphasic insulin dose response in adipocyte plasma membranes. This fluorometric assay for phosphatidylcholine represents an alternative method for monitoring phospholipid methylation, especially when increased sensitivity is required.

Adipose Tissue↗
PubMed1989

Phosphatidylglycerol in amniotic fluid. Comparison of an "ultrasensitive" immunologic assay with TLC and enzymatic assay.

Phosphatidylglycerol (PG) in amniotic fluid is recognized as a good indicator of fetal lung maturity and is unaffected by moderate amounts of blood or meconium contamination. A rapid immunologic agglutination assay, Ultrasensitive AmnioStat-FLM (FLM), was compared with two-dimensional thin-layer chromatography (TLC) and an enzymic, colorimetric procedure (E-PG). Eighty amniotic fluid specimens were analyzed. FLM results were reported as high (H), intermediate (I), or low positive (L). TLC was compared with FLM:H (n = 27), mean 0.14 (fraction of total phospholipids); I (n = 7), mean 0.11; L (n = 9), mean 0.03; negative results had no detectable PG by TLC. In 33 cases E-PG was compared with FLM:H (n = 9), mean 7.0 mumol/L; I (n = 5), mean 8.1 mumol/L; L (n = 3), mean 3.0 mumol/L; negative (n = 16), mean 3.2 mumol/L. Records were reviewed in 70 cases. Thirty cases were excluded: sample to delivery time was greater than 72 hours; steroids were given or sepsis was documented. Fetal lung immaturity was clinically present in six cases: respiratory distress syndrome in three cases and transient tachypnea of the newborn (TTN) in three cases. One false positive result was identified (TTN, FLM:H). FLM sensitivity for fetal lung maturity was 85.3%, specificity was 83.3%, and the positive predictive value for fetal lung maturity was 96.7%. FLM is a fast, reliable indicator of fetal lung maturity.

Agglutination Tests↗
PubMed1987

A method for the sequential colorimetric determination of serum triglycerides and cholesterol.

A simple spectrophotometric method for the sequential determination of triglycerides and cholesterol from a single serum sample was developed. In this two-stage procedure, the triglycerides and cholesterol esters are first hydrolysed to glycerol and free cholesterol respectively, with simultaneous scavenging of the liberated free fatty acids, a technique that ensures clarity of the sample. The glycerol is subsequently reacted to result in an intense red chromogen with a peak absorption maximum at 510 nm following a series of enzymic reactions. In the second stage, addition of cholesterol oxidase leads to oxidation of free cholesterol generated from the cholesterol esters in the first stage and the free cholesterol normally present in the sample, yielding in a similar fashion the identical red chromogen whose absorbance is also measured at 510 nm. Results obtained with the proposed method demonstrate good correlation with established individual procedures for triglycerides and cholesterol.

Bilirubin↗
PubMed1987

Problems with measurements caused by high concentrations of serum solids.

There have been numerous reports of spectrophotometric and volume problems caused by elevated levels of lipids in blood. The offending lipids, primarily triglycerides, not only cause turbidity leading to optical aberrations when added to analytical reagents, but also result in short-sampling errors leading to the measurement of inaccurate volumes of sample. Numerous methods have been developed to clear the lipemia, including ultracentrifugation organic solvent extraction, chemical precipitation and, most recently, enzymic hydrolysis. Although the latter procedures eliminate the optical problems, they do not deal with the volume dilution error created by the triglycerides. In turn, corrective mathematics have been developed to compensate for the inaccurate pipetting caused by the elevated lipids in a sample; however, these empirical calculations are not truly accurate at high concentrations of total lipids. This monograph will describe the problems caused by the presence of elevated lipids and the means available for treating them.

Blood Chemical Analysis↗
PubMed1986

On-line clarification for the measurement of serum glucose in hyperlipidemic specimens.

The optical aberrations due to the presence of the turbidity caused by hyperlipidemia has been eliminated in two serum glucose procedures. This has been accomplished by incorporating lipase and alpha-cyclodextrin into the two glucose reagents. The hydrolytic action of the lipase generates water soluble glycerol and insoluble fatty acids. By including the chemical scavenger alpha-cyclodextrin into the reagent the fatty acids are solubilized and thus the production of a second turbidity is avoided. Because the clearing reagents are incorporated into the glucose reagents, this is an on-line process and no additional labor is required to clear the sample-reagent mixture. Furthermore, no additional time is required as the clearing occurs in the same period of time that it takes for the indicator reactions to reach equilibrium.

Blood Glucose↗
PubMed1986

Enzymic clearing of lipaemic serum following total parenteral nutrition: determination of neonatal bilirubin as a model.

Bilirubin determinations in the newborn infant are one of the many analytical tests that can yield misleading results when the specimen is either iatrogenically or naturally lipaemic. Incorporation of a recently reported enzymic clarification system into a commercially available test kit enables one to conveniently and accurately quantify both total and direct bilirubin within the present procedural characteristics of the Bilirubin Stat Analyser Photometer. This instrument measures the former directly with bichromatic spectrophotometry and the latter with a conventional diazo-type reaction. The proposed modification of existing reagents allows one to apply the assay to samples with as much as, and possibly more than 16 g/l of triglycerides which has been introduced into the vascular circulation as intravenous total parenteral nutrition.

Bilirubin↗
PubMed1986

Potential problems in serum protein electrophoresis.

Potential problems are described that one could encounter in carrying out an electrophoretic procedure including its ancillary phases of visualization (staining) and quantification (densitometry). Endpoint-like measurements for separated isoenzymes may provide artifactual kinetic values as well, because stain measurement is fixed at a single time whereas reagent blanking in the electrophoretic medium is substituted for the conventional serum initial absorbance readings of test-tube determinations. Truncation of separated electrophoretic zones or opacity of an electrophoretic anti-convection medium such as uncleared cellulose acetate may also interfere with absolute quantification procedures.

Albumins↗
PubMed1986

A kinetic colorimetric procedure for quantifying magnesium in serum.

We have developed a kinetic colorimetric procedure for determination of magnesium in serum. The magnesium-dependent enzyme glycerol kinase is used to phosphorylate glycerol to glycerol 3-phosphate, the latter being oxidized to dihydroxyacetone phosphate and hydrogen peroxide by glycerophosphate oxidase. The generated hydrogen peroxide is then reduced by peroxidase with the simultaneous oxidative coupling of 4-aminoantipyrine and 2-hydroxy-3,5-dichlorobenzenesulfonate, producing a red reaction product with an absorption maximum at 510 nm. The rate of color production is proportional to the concentration of the Mg X ATP complex, which is, in turn, proportional to the magnesium concentration in serum. This method is rapid and precise, avoids the use of expensive instrumentation, is easily automated, and results compare well with those by the Du Pont aca and manual Magon sulfonate methods.

Autoanalysis↗
PubMed1986

The clinical use of alkaline phosphatase enzymes.

The enzyme alkaline phosphatase is an important serum analyte and its elevation in serum is correlated with the pressure of bone, liver, and other diseases. The analysis of the isoenzymes of alkaline phosphatase is an aid in diagnosing liver and/or bone disease, especially the high molecular weight isoenzymes that appear in cholestatic liver disease.

Alkaline Phosphatase↗
PubMed1985

The turbid specimen as an analytical medium: hemoglobin determination as a model.

The quantitation of chemical constituents in lipemic samples is a major problem confronting the clinical laboratory. Currently, a number of cumbersome and time-consuming methods are used to clarify samples before analysis. However, the use of enzymic hydrolysis of triglycerides along with efficient chemical removal of the formed non-esterified fatty acids is exemplified here as an excellent alternative to the current methods of clarification such as ultracentrifugation, extraction or chemical precipitation of low density and very low density lipoproteins. This method of clarifying milky serum has been used by us to assay hemoglobin in severely lipemic blood samples as an analytical model.

Chylomicrons↗
PubMed1985

The variable reagent blank: protein determination as a model.

Three total protein assays were analyzed to determine the extent of deviation encountered when a constant measured reagent blank is compared to a continuously decreasing true reagent blank. This blank effect owes its regressive nature to the consumption of the active reagent ingredient by the protein reactive species, variably and sometimes, with certain reactants, nonlinearly in the presence of increasing protein concentrations. However, the blank effect of interest here is apparent only when the reagent and the reagent-protein complex present overlapping spectra and therefore absorb at the wavelength of measurement. Thus it was found that while the biuret and the Coomassie brilliant blue assays produced pronounced differences in the variable true reagent blanks, the Folin-Ciocalteau reaction did not develop a deviation from the true blank since the reagent blank does not absorb to any extent at the assay wavelength. In this manner, the latter procedure could serve as a marker against which the former two blank reactions can be shown to display relatively excessive deviations.

Biuret Reaction↗
PubMed1985

Spectrophotometric investigation of sensitive complexing agents for the determination of zinc in serum.

Of two sensitive complexometric reagents for the colorimetry of serum zinc that we investigated, one, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP), was found to be a potentially useful compound for trace-metal determinations. It has a high molar absorptivity (120 000 L mol-1 cm-1) but is not convenient to use because it is not very soluble in water. The other reagent, a related pyridylazo compound, is 2-(5-bromo-2-pyridylazo)-5-(N-n-propyl-N-3-sulfopropylamino)phenol (5-BR-PAPS). It seems better suited for use in routine zinc determinations because, besides being water soluble, it has a higher molar absorptivity, 130 000 L mol-1 cm-1. Results by the proposed method developed with 5-Br-PAPS correlated well with those by atomic absorption spectrophotometry. The between-run CV for control sera was less than 5%; the within-run CV (same controls) was less than 4%.

Azo Compounds↗
PubMed1985

Three methods compared for determining phosphatidylglycerol in amniotic fluid.

Phosphatidylglycerol is one component of amniotic fluid that is unaffected by several of the reported interferences with conventional thin-layer chromatographic measurement of phospholipid. To compare a rapid immunological agglutination test, "Amniostat-FLM", with two-dimensional thin-layer chromatography, we determined phosphatidylglycerol by both methods in 41 amniotic fluid specimens obtained at 31 to 40 weeks of gestation. We also assayed phosphatidylglycerol in 14 of these specimens by an enzymic, colorimetric procedure. The agglutination test is rapid and simple but relatively insensitive; it yielded positive results for only seven of 23 specimens in which phosphatidylglycerol was detected by thin-layer chromatography. In 18 specimens in which no phosphatidylglycerol was detected by thin-layer chromatography, results by Amniostat-FLM were also negative; however, eight of these specimens, assayed by the enzymic method, had phosphatidylglycerol present. Apparently, the Amniostat-FLM detects phosphatidylglycerol only at concentrations exceeding 25 mumol/L, or more than 15% of the total phospholipid composition.

Agglutination Tests↗
PubMed1985

Peroxidase-coupled method for kinetic colorimetry of total creatine kinase activity in serum.

We describe a peroxidase-coupled method involving a colorimetric indicator reaction for determining the total activity of creatine kinase (EC 2.7.3.2) in serum. The kinetically favorable reverse reaction is exploited to generate adenosine 5'-triphosphate, which is used in the glycerol kinase-catalyzed phosphorylation of glycerol. The glycerol 3-phosphate so generated is oxidized in the presence of alpha-glycerophosphate oxidase to produce hydrogen peroxide, which is reduced in the presence of peroxidase with the simultaneous oxidation and coupling of 4-aminoantipyrene and 2-hydroxy-3,5-dichlorobenzenesulfonate to produce an intensely colored red chromogen. Results of the proposed method (y) correlate well with those of the Boehringer-Mannheim "CK-NAC UV" method as applied to the Hitachi 705 chemistry analyzer (y = 1.025 chi - 18.1, r = 0.9985, n = 100, range = 19-4531 U/L). The sensitivity of the method, based on molar absorptivities, is nearly fourfold that of procedures involving the reduction of NADP+.

Adenosine Triphosphate↗
PubMed1979

Investigation of reaction intermediates of the urea-diacetylmonoxime reaction.

1. An investigation of the intermediates of the urea-diacetylmonoxime reaction and the isolation of the protochromogen has been described. A comparative spectral study of the protochromogen with that of the literature values suggested the structure of the protochromogen to be a diureide. 2. The diureides of 1-phenyl-1,2-propanedione-monoxime and 2,3-pentanedione were synthesized and their visible, U.V., I.R., NMR, and mass desorption spectrometry data were analyzed. The study suggests that the structure of each of these compound is that of a diureide. When these diureides were redissolved in acid media, they gave the color expected of the corresponding chromogens found from the respective diketones and urea. 3. The 3a-methyl-6a-phenyl-glycoluril was synthesized by a base-catalyzed reaction. When this glycoluril was dissolved in concentrated HCl, a pink color was obtained, similar to that of the corresponding diureide. These studies indicate that both the diureide and the glycoluril (if formed at all in acid-catalyzed reaction) are converted to the same chromogen, possibly via a rearrangement. 4. When 2,3-butanedionemonoximethiosemicarbazone was reacted with urea in acid medium, characteristic spectral data were obtained which were very similar to those of the urea-diacetylmonoximethiosemicarbazide reaction. This tends to indicate that the possible structures of the protochromogens are similar and of the open chain diureide type.

Acetone↗