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.

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.

Liquid-chromatographic assay of urinary porphobilinogen

This is a rapid (10 min per sample), highly sensitive procedure for quantifying urinary porphobilinogen (PBG). Interfering substances are removed by selectively adsorbing PBG onto an ion-exchange resin. After PBG is eluted with 0.5 mol/L formic acid, Ehrlich's reagent is added to produce the chromophore, which is then injected into a liquid chromatograph equipped with a diode-array detector. PBG is separated by a linear gradient (10% to 100%) of methanol in 10 mmol/L phosphate buffer, pH 3.0. Absorbance is monitored at 555 nm. Assay response varies linearly with PBG concentration over the range 0-110 mumol/L (0-25 mg/L). As little as 1.5 mumol/L (0.3 mg/L) can be detected. In prepared urine samples with known PBG concentrations, the within-run coefficient of variation (CV) ranged from 1.7% to 3.2%, the day-to-day CV from 3.5% to 6.1%. PBG concentrations in 24-h urine collected from 25 healthy subjects were all below the detection limit of the assay (less than 1.5 mumol/L). We used the new assay to measure PBG concentrations in the urine of two patients with latent porphyria. This method is more sensitive than spectrophotometric techniques currently used for measuring urinary PBG.

Liquid-chromatographic assay of urinary porphobilinogen

This is a rapid (10 min per sample), highly sensitive procedure for quantifying urinary porphobilinogen (PBG). Interfering substances are removed by selectively adsorbing PBG onto an ion-exchange resin. After PBG is eluted with 0.5 mol/L formic acid, Ehrlich's reagent is added to produce the chromophore, which is then injected into a liquid chromatograph equipped with a diode-array detector. PBG is separated by a linear gradient (10% to 100%) of methanol in 10 mmol/L phosphate buffer, pH 3.0. Absorbance is monitored at 555 nm. Assay response varies linearly with PBG concentration over the range 0-110 mumol/L (0-25 mg/L). As little as 1.5 mumol/L (0.3 mg/L) can be detected. In prepared urine samples with known PBG concentrations, the within-run coefficient of variation (CV) ranged from 1.7% to 3.2%, the day-to-day CV from 3.5% to 6.1%. PBG concentrations in 24-h urine collected from 25 healthy subjects were all below the detection limit of the assay (less than 1.5 mumol/L). We used the new assay to measure PBG concentrations in the urine of two patients with latent porphyria. This method is more sensitive than spectrophotometric techniques currently used for measuring urinary PBG.

Agarose gel patterns of alkaline phosphatase isoenzymes before and after treatment with neuraminidase

The clinical value of alkaline phosphatase isoenzyme analysis is limited by the inability of most electrophoretic methods to resolve the liver and bone isoenzymes. The authors attacked this problem by treating serum samples with neuraminidase, then running treated and untreated samples side-by-side on specially prepared agarose gels. Each isoenzyme showed a characteristic mobility before and after neuraminidase treatment that allowed its identification. The mobility of the bone isoenzyme was most affected, whereas the intestinal isoenzyme was resistant to the action of neuraminidase. In samples with both liver and bone isoenzymes, pretreatment with neuraminidase clearly distinguished the bands, allowing quantitation by densitometry. Using this method, the authors discovered 22 liver isoenzymes in 54 samples that were interpreted as only bone isoenzyme before neuraminidase treatment. They also detected two bone isoenzymes in 35 samples that appeared to contain only liver +/- biliary isoenzymes. In addition, this procedure enabled them to characterize several unusual isoenzymes with respect to mobility, thus avoiding confusion with the other isoenzymes.

A rapid and accurate spectrofluorometric method for quantification and screening of urinary porphyrins

We describe a fluorescence method for screening and quantifying urinary porphyrins. New and effective approaches are used to oxidize prophyrinogens, correct the baseline, and ensure that uroporphyrin (uro) and coproporphyrin (copro) are equally detected, mole for mole. No preliminary purification is required. A 45-microL aliquot of urine is oxidized with 3 mmol/L iodine in 3 mol/L HCl to convert porphyrinogens to porphyrins, and then decolorized with 5 mL of 0.45 mmol/L sodium thiosulfate. An excitation scan is done from 350 nm to 440 nm, monitoring emission at 650 nm. Total porphyrin content is determined at the isosbestic point for uro and copro, and the mole fractions of uro and copro are estimated from the wavelength of the signal maximum. There is no interference from protein, glucose, bilirubin, or hemoglobin in high concentration. The limit of detection is less than 30 nmol/L and linearity is maintained up to 3200 nmol/L. Recoveries and precision are excellent. This is a rapid, sensitive screen for porphyrinuria as well as an accurate and precise quantitative method. We compared the method with existing methods and discuss some shortcomings common to many of them.

A rapid and accurate spectrofluorometric method for quantification and screening of urinary porphyrins

We describe a fluorescence method for screening and quantifying urinary porphyrins. New and effective approaches are used to oxidize prophyrinogens, correct the baseline, and ensure that uroporphyrin (uro) and coproporphyrin (copro) are equally detected, mole for mole. No preliminary purification is required. A 45-microL aliquot of urine is oxidized with 3 mmol/L iodine in 3 mol/L HCl to convert porphyrinogens to porphyrins, and then decolorized with 5 mL of 0.45 mmol/L sodium thiosulfate. An excitation scan is done from 350 nm to 440 nm, monitoring emission at 650 nm. Total porphyrin content is determined at the isosbestic point for uro and copro, and the mole fractions of uro and copro are estimated from the wavelength of the signal maximum. There is no interference from protein, glucose, bilirubin, or hemoglobin in high concentration. The limit of detection is less than 30 nmol/L and linearity is maintained up to 3200 nmol/L. Recoveries and precision are excellent. This is a rapid, sensitive screen for porphyrinuria as well as an accurate and precise quantitative method. We compared the method with existing methods and discuss some shortcomings common to many of them.

Precipitation of serum proteins by the lectin from wheat-germ

We investigated the composition of the precipitate that forms when wheat-germ lectin derived from Triticum vulgaris is added to serum. A number of serum proteins are precipitated, representing about 2.5% of the total serum protein. This study demonstrates that the interaction of this lectin with the bone isoenzyme of alkaline phosphatase is not specific.

Precipitation of serum proteins by the lectin from wheat-germ

We investigated the composition of the precipitate that forms when wheat-germ lectin derived from Triticum vulgaris is added to serum. A number of serum proteins are precipitated, representing about 2.5% of the total serum protein. This study demonstrates that the interaction of this lectin with the bone isoenzyme of alkaline phosphatase is not specific.

Alkaline phosphatase isoenzymes resolved by electrophoresis on lectin-containing agarose gel

With this electrophoretic method the liver, biliary, and bone isoenzymes of alkaline phosphatase are clearly separated on agarose gels. Wheat-germ lectin, incorporated in the gel matrix, binds the bone isoenzyme selectively, forming a precipitate near the origin. Neither liver nor biliary isoenzyme is affected. Activity staining with an indigogenic dye substrate reveals the liver isoenzyme migrating nearest the anode, followed by the biliary and bone isoenzymes. Results are generally similar to those of electrophoresis on cellulose acetate. However, the lectin-agarose gels better resolve the liver and bone isoenzymes, and heat treatment of samples is not required before electrophoresis.

Alkaline phosphatase isoenzymes resolved by electrophoresis on lectin-containing agarose gel

With this electrophoretic method the liver, biliary, and bone isoenzymes of alkaline phosphatase are clearly separated on agarose gels. Wheat-germ lectin, incorporated in the gel matrix, binds the bone isoenzyme selectively, forming a precipitate near the origin. Neither liver nor biliary isoenzyme is affected. Activity staining with an indigogenic dye substrate reveals the liver isoenzyme migrating nearest the anode, followed by the biliary and bone isoenzymes. Results are generally similar to those of electrophoresis on cellulose acetate. However, the lectin-agarose gels better resolve the liver and bone isoenzymes, and heat treatment of samples is not required before electrophoresis.

Fibrinogen Seattle II: defective release of fibrinopeptide A in a slow clotting fibrinogen

A functionally abnormal fibrinogen was detected in a 27-year-old woman with no prior history of bleeding. Investigation of the defect revealed abnormal release of fibrinopeptide A and incomplete polymerization of fibrin monomers. Crosslinking of polymerized fibrin by Factor XIII was normal. To further characterize the dysfibrinogen, the increase in mechanical impedance during clot development was measured. Fibrinogen Seattle II showed several differences from normal fibrinogen: delayed onset of clotting, decreased rate of clot formation, and lower final clot impedance. Taken cumulatively, these data are consistent with an amino acid substitution at or near residue 16 in one of the A alpha chains, the point at which thrombin cleaves.

Application of mechanical impedance measurements to the study of dysfibrinogens

Most techniques of clot detection do not give information about the mechanical properties of the forming clot. A procedure was developed by which the dynamic loss modulus, or mechanical impedance, of a solution of fibrinogen could be continuously monitored during clot development. This method was then applied to the analysis of purified preparations of normal fibrinogen and two dysfibrinogens. Both thrombin and reptilase were used as clotting agents, and unique tracings of clot impedance vs. time were generated for each dysfibrinogen. The functional defect was known in each case, and the clot impedance tracings were able to distinguish between abnormalities in the release of fibrinopeptides A and B. Mechanical impedance measurements were shown to complement other types of analyses now used in the characterization of dysfibrinogens. In particular, they distinguished between dysfibrinogens that appeared similar by more conventional laboratory methods.

Liquid-chromatographic profiles of urinary porphyrins

Information on changes in the urinary excretion pattern of porphyrins can be especially useful in the diagnosis of disorders of porphyrin metabolism. Most clinical laboratory procedures are designed for assay of uroporphyrin and coproporphyrin only, and in many cases even these are not cleanly separated. Hence, we developed a "high-performance" liquid-chromatographic procedure to separate and quantify all five urinary porphyrins--that is, those with four through eight carboxyl groups. Before chromatography, the porphyrins are isolated from other urinary components by two simple, rapid pretreatment steps, then injected into the chromatograph in nonesterified form. They are separated and eluted with a step gradient of methanol/phosphate buffer, pH 3.0, in which the methanol content is first 650, then 850 mL/L. As little as 1 ng of eluted porphyrins can be measured fluorometrically. Analytical recovery of coproporphyrin is virtually 100% and of uroporphyrin 75-80%. CVs are about 10% for coproporphyrin at 70 micrograms/L and 20-40% for uroporphyrin at 8 micrograms/L.

Liquid-chromatographic profiles of urinary porphyrins

Information on changes in the urinary excretion pattern of porphyrins can be especially useful in the diagnosis of disorders of porphyrin metabolism. Most clinical laboratory procedures are designed for assay of uroporphyrin and coproporphyrin only, and in many cases even these are not cleanly separated. Hence, we developed a "high-performance" liquid-chromatographic procedure to separate and quantify all five urinary porphyrins--that is, those with four through eight carboxyl groups. Before chromatography, the porphyrins are isolated from other urinary components by two simple, rapid pretreatment steps, then injected into the chromatograph in nonesterified form. They are separated and eluted with a step gradient of methanol/phosphate buffer, pH 3.0, in which the methanol content is first 650, then 850 mL/L. As little as 1 ng of eluted porphyrins can be measured fluorometrically. Analytical recovery of coproporphyrin is virtually 100% and of uroporphyrin 75-80%. CVs are about 10% for coproporphyrin at 70 micrograms/L and 20-40% for uroporphyrin at 8 micrograms/L.

Complete amino acid sequence of human brain calmodulin

The complete amino acid sequence of calmodulin from human brain has been determined by using peptides derived from digests with trypsin. Staphylococcus aureus V8 protease, and cyanogen bromide. The peptides were purified by means of reversed-phase high-performance liquid chromatography and analyzed with a sequenator. The protein contains 148 amino acid residues and has a molecular weight of 16792. As in other calmodulins, the amino-terminal residue of the protein is blocked by an acetyl group, and a trimethyllysine residue is located at position 115. The only difference between this sequence and those fully determined in other species is the assignment of amide groups.