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Spinal fluid protein revisited: a reappraisal of the biuret procedure.

In this study our previously described selected method, a biuret procedure with deproteinization, for the determination of spinal fluid protein is thoroughly discussed against the background of the results found with a number of Lowry modifications. The use of various separation techniques, i.e. deproteinization, ultrafiltration and chromatography (HPLC), for protein analysis led to the question as to whether low molecular weight proteins in cerebrospinal fluid play an important role or not with respect to the choice of a selected method for the determination of total protein.

Biuret Reaction↗

Effects of dextran on five biuret-based procedures for total protein in serum.

We evaluated the effect of dextran on values for total protein in serum as measured by the biuret method with five widely used automated instruments: the American Monitor Parallel; the Du Pont aca II; the Roche Cobas-Bio; the Kodak Ektachem 400; and the Beckman Astra 8. Dextran concentrations as great as 25 or 30 g/L had relatively little or no influence on total protein measurements by the latter three instruments. Dextran concentrations exceeding 6 g/L caused falsely low results with the aca, whereas the Parallel gave falsely high results when the dextran concentration exceeded 2 g/L. The aca total protein procedure could be protected from the interference by dextran concentrations up to 30 g/L by injecting 0.4-0.8 mL of ethylene glycol directly into the reagent pack before sampling. However, we could not eliminate the interference with the Parallel procedure by any simple means; we thus recommend that it not be used for measuring total protein in serum samples from patients who are being treated with dextran.

Adult↗

[The use of different albumin preparations as calibrators in determining the total protein in blood serum by the biuret method].

The authors have investigated the possibility of using various albumin preparations as calibrators in measurements of human blood serum total protein by the biuret method. Analysis of Precinorm U and Precipath U reference sera has demonstrated that use of various albumin preparations as calibrators may result in significant deviations (as much as 27%) of the resultant values from the due ones.

Biuret Reaction↗

The quantitation of urinary and spinal fluid proteins by a modified biuret method.

A method is presented for the quantitation of urinary and CSF protein. In the presence of 0.10 N NaOH the peptide bonds of the protein remove and bind copper from an ion exchange resin. The resulting copper-protein complex is separated from low molecular weight substances by gel filtration and the copper in the eluted complex is determined colorimetrically with diethyldithiocarbamic acid. The method requires only 100mul of sample, has biuret specificity and uses a single prepacked column. The limit of sensitivity is 2 mg of protein per deciliter.

Cerebrospinal Fluid Proteins↗

[Determination of proteins with the Coomassie brilliant blue G 250 method. III. Behavior of various pure proteins and comparative analysis with the biuret and Lowry methods].

Some proteins were tested by the Bradford's method with Coomassie Brilliant Blue G 250. The findings were compared to those obtained by the Lowry's and the biuret methods. Coomassie, as the other methods, has the inconvenient of giving different absorbaces according to the nature of single protein. The use of standards of analogous composition in assaying proteins by the Bradford's method is suggested.

Animals↗

Optimization of the conditions for biuret complex formation for the determination of peptides by capillary electrophoresis with ultraviolet detection.

Capillary electrophoresis with UV detection was utilized to optimize copper complexation conditions for the analysis of neuropeptides. Complexation was confirmed by monitoring the response at a visible wavelength. Four complexation strategies were used to compare the UV response of native peptides and their respective copper complexes. All four strategies resulted in complete complexation, but on-capillary complexation provided significant advantages over precapillary and pre-/on-capillary. An increase in UV absorbance along with peak stacking resulted in a significantly greater response using the on-capillary technique. Also, on-capillary complexation does not require dilution of the sample. The effects of temperature and copper concentration were also investigated. The utility of this method for the separation of an enkephalin peptide mixture is presented.

Angiotensin II↗