Expeditious assembly of biuret-guanidine derivatives via the catalyst-free transformation

We disclose a mild and practical catalyst-free transformation for the expeditious construction of biuret-guanidine derivatives using aromatic isocyanates. This synthetic transformation is featured with mild reaction conditions and high efficiency.

Comparison of plasma total solids concentration as measured by refractometry and plasma total protein concentration as measured by biuret assay in pet rabbits and ferrets

OBJECTIVE

To determine the agreement between plasma total solids (TS) concentration as measured by refractometry and plasma total protein (TP) concentration as measured by biuret assay in pet rabbits and ferrets.

SAMPLE

253 and 146 blood samples from 146 and 121 ferrets and rabbits, respectively, with results of CBC and plasma biochemical analyses.

PROCEDURES

Data were collected from medical records regarding plasma TS and TP concentrations, PCV, plasma biochemical values, plasma appearance, and patient signalment. Agreement was determined between refractometer and biuret assay (reference method) values for plasma TS and TP concentration. Other variables were examined for an impact on this agreement.

RESULTS

Mean ± SD plasma TP and TS concentrations were 6.4 ± 0.8 mg/dL and 6.6 ± 0.8 mg/dL, respectively, for rabbits and 6.3 ± 1.2 mg/dL and 6.4 ± 1.1 mg/dL for ferrets. On average, refractometer values overestimated plasma TP concentrations as measured by biuret assay. Plasma cholesterol, glucose, and BUN concentrations and hemolysis and lipemia had significant effects on this bias for ferrets; only BUN concentration had an effect on bias for rabbits given the available data. Other variables had no influence on bias. The limits of agreement were wider than the total allowable analytic error, and > 5% of the data points were outside acceptance limits, indicating that the 2 methods were not in clinical agreement.

CONCLUSIONS AND CLINICAL RELEVANCE

Refractometer measurements of plasma TS concentration failed to provide a good estimation of biuret assay measurements of plasma TP concentration in rabbits and ferrets, suggesting that these 2 analytic methods and the results they yield cannot be used interchangeably in these species.

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.

Determination of the pharmaceutical peptide TP9201 by post-column reaction with copper(II) followed by electrochemical detection

An electrochemical detection method was applied to the determination of the synthetic peptide TP9201 (Telios Pharmaceuticals). The method utilizes reversed-phase HPLC, followed by post-column formation of Cu(II)-peptide complexes to render peptides electrochemically active via the Cu(III/II) couple. TP9201 is cyclic and N-amidated; the lack of a free amine precludes the use of typical fluorescent labeling reagents. Neither the cyclic structure nor the N-amidation prevented the copper complexation reaction, however. The detection limit in bovine serum was 20 nM, limited by interfering sample peaks, and the detector response was linear in a range 10-400 nM.

Automated procedures for the quantitation of protein

An entirely automated 96-well microplate-based system to perform procedures for the measurement of protein is described. This single instrument system utilizes a series of computer-controlled mechanical subsystems to move the plate, control incubations and dispense samples or reagents in order to perform the assay. This system allows the investigator to reproducibly perform these protein assays on large numbers of biological samples with minimal effort.

Methylisocyanate and actin polymerization: the in vitro effects of carbamylation

Uremia has been implicated in cataractogenesis due to protein carbamylation by cyanate derived from urea. The present study was designed to directly identify the effects of carbamylation on actin polymerization and the possible contribution to cataract formation. The susceptibility of actin to carbamylation is expected because of the 19 lysines distributed along its length. The lysines of actin were selectively carbamylated by methylisocyanate (MIC) at pH 8.0 and 4 degrees C and actin polymerization assayed by high-shear viscometry, fluorescence and transmission electron microscopy. Our results provide evidence that non-enzymatic carbamylation of the lysine residues prevents the polymerization of actin. In addition, this carbamylated actin inhibited the polymerization of nascent, unmodified actin. High-shear viscosity measurements demonstrated decreased initial apparent rates and decreased steady-states (final specific viscosities) of polymerization. Fluorescence measurements showed decreased relative intensities of fluorescence versus control and confirmed the inhibitory effects of carbamylation by MIC on the steady state of F-actin. Transmission electron microscopy (TEM) showed the presence of disorganized filaments when carbamylated actin was added to polymerizing unmodified actin. Our results suggest that carbamylation of actin can cause a loss of ordered filament structure and shape of the lens fiber cell, thus predisposing it to cataract development.

Electrochemical detection of oligopeptides through the precolumn formation of biuret complexes

The relatively slow kinetics of formation of the electroactive Cu(II)-peptide complexes from larger (greater than 6 amino acids) peptides requires relatively high temperature and long reaction times for a postcolumn reactor. The precolumn incubation of bradykinin, Tyr8-bradykinin and insulin A chain with biuret reagent for 20 min at 60 degrees C leads to the formation of biuret complexes which can be subjected to chromatography in acidic or basic eluents. These complexes are detected electrochemically with a sensitivity similar to the Cu(II)-(ala)3 complex (1 nC/pmol at 1.0 ml/min). The influence of the column-packing material on the electrochemical detector response of the Cu-peptide complexes has also been studied.

Application of a silver-binding assay to the determination of protein in cerebrospinal fluid

We evaluated a silver-binding assay for use in measuring total protein in cerebrospinal fluid. The advantage of this procedure over other methods is that, because of its sensitivity, it requires only a 0.5-microL sample. The procedure, which takes approximately 40 min to complete, involves dilution of 0.5-microL samples to 1 mL with distilled water containing sodium dodecyl sulfate, followed by addition of glutaraldehyde and an ammoniacal silver solution. After color development for 30 min, the reaction is terminated with sodium thiosulfate and the absorbance is measured at 420 nm. This assay displayed within-run and day-to-day precision (CV) of 3.1% to 13% over the range of 210 to 1370 mg/L. It showed substantially less protein-to-protein variation than the Coomassie Blue dye-binding procedure when tested with albumin, globulin, and transferrin. It also yielded an accurate estimation of hemoglobin. Moreover, preliminary studies suggested that it was capable of quantifying immunoglobulin light chains and glycoproteins. In a study of 54 human cerebrospinal fluid samples, results of the silver-binding assay corresponded more closely with those obtained with a rate biuret assay (intraclass correlation coefficient = 0.91) than did either the dye-binding or classical Lowry methods.

Determination of chicken and turkey plasma and serum protein concentrations by refractometry and the biuret method

Plasma and serum protein concentrations were determined in chickens and turkeys by refractometry (with human and veterinary refractometers) and by the biuret method. Chicken and turkey serum protein values were significantly lower than respective plasma protein values according to both methods. Refractometer readings for both plasma and serum correlated closely with the results of the biuret test (r2 = 0.72 to 0.97). These findings indicate that plasma and serum protein values may be determined accurately in chickens and turkeys with a handheld refractometer.

Three turbidimetric methods for determining total protein compared

We used human serum protein fractions to evaluate the sensitivity and bias of three turbidimetric methods for determining concentrations of proteins. Each fraction (Cohn Fractions II, III, IV, and V) was assigned a protein concentration value that was determined by the biuret method, which we calibrated with purified monomer of human serum albumin. All three turbidimetric methods (those involving sulfosalicylic acid/sodium sulfate, trichloroacetic acid, and alkaline benzethonium chloride) gave acceptable results for Fraction V with crystallized human serum albumin as the reference material, but there was bias by each of the three methods for the three globulin fractions. The method involving alkaline benzethonium chloride with measurement at 450 nm had the best sensitivity within the range of linearity and the most consistent bias among the three globulin fractions. These results define the dilemma for valid calibration of these methods for total serum protein in cerebrospinal fluid and urine.

Evaluation of the Coomassie Brilliant Blue G-250 method for urinary protein

The Coomassie Brilliant Blue G-250 method for protein in urine has been evaluated for analytical accuracy and clinical applicability. Extremely simple to perform, the test exhibits good precision and sensitivity. The color developed per gram of protein is protein-type dependent, so no single protein standard is completely satisfactory. Color intensity is linearly related to concentration up to 1500 mg/L when used with a manual bichromatic method. Accuracy was clinically acceptable for patients with a variety of protein-losing diseases, and for patients having received renal transplants; however, the method underestimates urinary light-chain proteins. In athletes and premature neonates, we observed increased protein excretion during periods of stress. The upper reference limit for protein excretion in healthy adults is about 120 mg/24 h.

An improved modification of the biuret method for the determination of protein in turbid materials with high lipid and hemoglobin content

The quantitative determination of protein by means of the biuret method frequently yields erroneous values, especially when applied to turbid, lipid- and hemoglobin-containing materials. These errors can only partially be abolished either by the addition of detergents or by destroying the Cu-protein complex by KCN addition. It was found that most disturbances were almost completely eliminated after prior precipitation of protein by the addition of Triton X-100 to the solubilizing biuret reagent and absorbance measurements being performed at a wavelength of 572 nm before and after the addition of KCN. Values of protein determinations according to the proposed assay and protein concentrations calculated from Kjeldahl nitrogen determinations have been shown to agree fairly satisfactory. The proposed assay represents a relatively simple and versatile approach for the evaluation of protein concentrations in a variety of materials containing lipids, hemoglobin and of some other turbidities as well.

Assay of cerebrospinal fluid protein: a rate biuret method evaluated

We evaluated a rate colorimetric method (Beckman) for measuring total protein in cerebrospinal fluid. The automated instrument we used was Beckman's ASTRA TM. A 100-microL sample of spinal fluid is introduced into the biuret reagent in the reaction cell and the increase in absorbance at 545 nm is monitored for 20.5 s. Solid-state circuits determine the rate of alkaline biuret-protein chelate formation, which is directly proportional to the total protein concentration in the sample. The linear range of measurement is 120 to 7500 mg/L. Day-to-day precision (CV) over the range of 150 to 1200 mg/L ranged from 15.2 to 2.3%. The method was unaffected by radical alteration of the albumin/globulin ratio, but there is a positive interference in the presence of hemoglobin, a suppression in the presence of bilirubin, and no effect by xanthochromia. The method is precise, accurate, rapid, and convenient. The method was compared with the trichloroacetic acid method as performed on the Du Pont aca III, giving a correlation coefficient (r2) of 0.9693. The method is precise, accurate, rapid, and convenient.

[Quantitative determination of total urinary protein utilizing the principle of Coomassie Brilliant Blue G250 binding to protein (author's transl)]

Coomassie Brilliant Blue G250 was used for the determination of total urinary protein and compared with the biuret-procedure. In the Coomassie Brilliant Blue G250-assay 0.10 ml urine are added to 5.0 ml Coomassie Brilliant Blue G250 reagent and the sample is read against the reagent blank. The Coomassie Brilliant Blue G250 method seems to be superior to the biuret-procedure because of better reproducibility, higher sensitivity and simpler handling. The upper limit or urinary protein excretion in 49 healthy subjects was 120 mg/24 h. To evaluate the clinical significance of the Coomassie Brilliant Blue G250 method the urinary protein concentration of 134 patients with metabolic, systemic and organ diseases was compared with the biuret-procedure. The regression line was y = 0.827 X + 8.713 mg/l with a correlation coefficient of r = 0.966. The type of proteinuria (mixed, glomerular, tubular) had no influence on the protein value measured with the Coomassie Brilliant Blue G250 method. However in selective proteinuria, like Bence-Jones protein excretion, there is no correlation between the two methods, because the concentration of Bence-Jones protein is underestimated. Lower protein values were also frequently obtained for patients with diabetes mellitus. Some specimens from patients with chronic renal failure treated by haemodialysis showed elevated values. In spite of these limitations the Coomassie Brilliant Blue G250 method might become the method of choice for the determination of total urinary protein.

Spectrophotometric study of total protein-albumin methods applied to cerebrospinal fluid

A spectrophotometric study was carried out for three proteins assays when modification of their serum procedures using bromcresol green, bromcresol purple and biuret reagents were applied to the determinations of total proteins and albumin in cerebrospinal fluids. A novel concentration device wherein the sample itself was used as the primary diluent for the three reagents concentrated to contain the proper amounts of chemicals in smaller volumes than suggested in their serum procedures allowed reasonable absorbance signals to be obtained. Low molecular weight molecules were separated from the albumin and globulins of the fluids by centrifugal ultrafiltration using a 25K cutoff and spectra were obtained for both high and low molecular weight fractions. Some materials were obtained in the separated ultrafiltrates which gave reactions with all three reagents, reactions which either overlapped the spectra of the albumin reactions or superimposed the spectra obtained with the total protein reaction. A screening procedure for cerebrospinal fluid total proteins or centrifugally ultrafiltered albumin appears reasonable as an inference from studies made, although further elucidation of the low molecular weight fractions in needed as a confirmation device.

Amounts and sources of protein for dairy calves

Female Holstein calves (178) were fed rations varying from 10 to 17% crude protein (air dry) from 30 to 102 days of age. Ten percent was inadequate resulting in less body weight, gain, withers height, and heart girth than rations containing 12 to 17% crude protein. In trial 1 addition of urea, biuret, or ammonia-molasses to a 12% diet to make a 16% crude protein diet allowed gains and weights indistinguishable from those on a 12 or 16% crude protein soybean meal ration. In another trial, addition of urea, biuret, or ammonium propionate to a 10% ration to make a 14% ration allowed insignificantly greater gains and body weight. Gains and body weight were greater for the 14% soybean meal ration than the three non-protein-nitrogen rations for calves to 71 days of age but equal for 71 to 102 days. Gain, body weight, dry matter, and protein intakes at most dates and intervals were greater for calves fed the 14% soybean meal ration than the 10% ration. When 10, 12, 14, and 16% soybean meal rations were compared simultaneously, only the 10% crude protein ration gave inferior performance. Gains were reduced when average daily crude protein intake for the 72 day trail was 258 g or less. Calves fed lupine or dried poultry waste did not gain or consume as much as those fed comparable soybean meal rations. Calves fed a 17% crude protein ration from several protein sources plus alfalfa hay gained no much than those fed the 12 to 16% crude protein rations. Regression analysis relating dry matter and protein intake to body weight or gains indicated both dry matter intake and protein percentage were about equally important from day 41 to 72 and that after this age dry matter intake was of much greater importance than protein percentage. Protein intake expressed as g/day was not of importance in this regression. Weaning at day 42 allowed for greater body weight and gains than weaning at day 32. The difference in body weight was 2.5 kg at day 42 and 7 kg at day 102.

Comparison of three methods for plasma fibrinogen

Three plasma fibrinogen methods are presented based on (1) clottable protein assay by Biuret reagent, (2) measurement of clot absorbance and (3) thrombin time. These methods show good correlation and adequate precision on normal subjects as well as heparinized plasmas. The effects of interference owing to hemolysis, lipemia, bilirubin, heparin and fibrinogen degradation products are discussed briefly.