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PubMed1994

Proteolytic degradation of low-density lipoprotein by lipoprotein(a) and by recombinant apo(a).

The plasma concentration of lipoprotein(a) (Lp(a)) is correlated with the risk of atherosclerosis, and both Lp(a) and LDL are present in atherosclerotic lesions. Lp(a) is similar in structure to LDL, its distinguishing feature from LDL being the presence of one additional glycoprotein, apo(a), that is linked to apoB-100. Upon incubation of 125I-LDL with isolated Lp(a), we found a dose and time-dependent increase in the proportion of TCA-soluble radioactive material, demonstrating degradation of LDL. The addition of unlabelled LDL decreased the degradation of 125I-LDL, while HDL or albumin had no such effect. Recombinant DNA-derived apo(a), R-apo(a), which itself expressed no amidolytic activity, displayed an increase in amidolytic activity after pre-incubation with LDL. Furthermore, activated R-apo(a) caused degradation of 125I-LDL. Treatment of R-apo(a) with phenylmethanesulfonyl fluoride inhibited LDL apoB-100 degradation, indicating that R-apo(a) has serine esterase type proteolytic activity. The results show that apo(a) is activated in the presence of LDL, and that this activation leads to proteolytic modification of LDL. The induction of apo(a) proteolytic activity by LDL suggests a novel mechanism whereby Lp(a) may be atherogenic.

Amino Acid Sequence↗
PubMed1980

Determination of free and esterified cholesterol by a kinetic method. II. Evaluation of the enzymic method which uses 2,2-azino-di(3-ethyl-benzthiazoline-6-sulfonate) (ABTS) as chromogen.

A simple kinetic method for the determination of free and esterified serum cholesterol based on the oxidation of 2,2'-azino-di(3-ethyl-benzthiazoline-6-sulfonate) (ABTS) by use of choilesterol esterase, cholesterol oxidase and peroxidase has already been reported. Here the method is statistically examined. The method is very sensitive and precise (C.V. below 5%). The standard curve is linear up to 25.9 mmol/l. Comparison with results by Abell's method gave a linear regression of Yx = 0.2025 + 1.0043X with a correlation coefficient (r) of 0.983. Comparison with the enzymic methods of Roeschlau et al., Trinder, and Allain et al. gave Yx = 0.2037 + 0.9549X (r = 0.975), Yx = 0.4777 +0.8857X (r = 0.958) and Yx = 0.244 + 0.932X (r = 0.970), respectively. The effects of haemoglobin and bilirubin were studied and normal ranges for the method were determined on 150 healthy mature subjects of both sexes between 20 and 45 years of age. They are 3.375 to 6.948 mmol/l for total cholesterol, and 0.7196 to 2.089 mmol/l for free cholesterol.

Adult↗
PubMed1980

The assay of factor V in plasma using a synthetic chromogenic substrate.

An analytical procedure using a synthetic substrate was devised for the determination of factor V in plasma. Factor V was activated by the reaction of immunobilized thrombin and incubated with an optimal concentration of a factor Xa, phospholipid, calcium and prothrombin. The thrombin generated was determined with the chromogenic substrate (Testzym S-2238). The initial rate of hydrolysis of the substrate was directly proportional to the factor V concentration. Effectors in plasma, such as prothrombin, fibrinogen, antithrombins and bilirubin, were controlled to minimize their effects. The normal value of factor V was from 3.3 to 5.5 units.

Chromogenic Compounds↗
PubMed1980

Improvements in the determination of urea using diacetyl monoxime; methods with and without deproteinisation.

A rapid and reproducible method is described for measurement of urea in biological materials (after deproteinisation) and in serum (without deproteinisation). Urea is colorimetrically determined with diacetyl monoxime and thiosemicarbazide in the presence of sulphuric acid, phosphoric acid and ferric chloride. The sensitivity of the colorimetric reaction and stability of the colour are enhanced over existing related procedures and the serum blank diminished, enabling urea to be precisely measured in micro amounts (1--5 microliters) of serum.

Chromogenic Compounds↗
PubMed1980

Evaluation of serum creatinine measurement by the direct acidification method for errors contributed by non-creatinine chromogens.

Serum creatinine determination by the direct acidification method was found to be non-specific. Chromogens other than creatinine could react with alkaline picrate and their developed color was also destroyed by acid. Only elevated levels of bilirubin and acetoacetate caused a significant interfering effect. The degree of this interference depended on: (1) the amount of the interfering substance; (2) the reaction time allowed for color development; and (3) the final acidity for decolorization.

Acetoacetates↗
PubMed1981

Quantitative endotoxin determination in blood with a chromogenic substrate.

A method is described for the quantitative determination of endotoxins in blood. The method is based upon the endotoxin-dependent activation of a proenzyme present in Limulus amebocyte lysate. This activated enzyme is measured by using the chromogenic substrate S 2422. Inhibitors and activated coagulation factors possibly interfering in the assay are removed by dilution and boiling. The method has been proven to be fast (2.5 h), sensitive and reproducible with a detection limit of 10 ng/l. Preliminary results comparing the results of blood cultures with the endotoxin assay indicate a good correlation.

Bacteria↗
PubMed1982

Interindividual variation in relationships between plasma heparin concentration and the results of five heparin assays.

In order to determine their value for estimating the heparin concentration in plasma, we established the relationship between test result and heparin concentration in plasma from various individuals, for five assays used with heparin treatment. Only assays which can be carried out routinely in clinical laboratories were considered. The thrombin time and the whole blood recalcification time give pointless and ambiguous information respectively, concerning the heparin level. The activated partial thromboplastin time with and without heparin neutralisation give only a rough estimate. The spectrophotometric method using a chromogenic substrate gives the best information. The latter can be improved by using a non-linear (parabolic) equation for the calculation of the reference curve. Current heparin therapy, controlled with the aid of a clotting assay, may result in plasma heparin concentrations that vary widely from one patient to another.

Blood Coagulation Tests↗
PubMed1982

Proposal for the standardization of the serum unsaturated iron binding capacity assay, and results in groups of subjects with normal iron stores and with prelatent, latent, and manifest iron deficiency.

An effort has been made to standardize the indirect iron saturation excess method for the determination of the serum unsaturated iron binding capacity (UIBC) and thus to relinquish the direct adsorption methods for the assay of the serum total iron binding capacity (TIBC) which give falsely high results due to unspecific binding of the saturating iron to serum proteins. In order to eliminate the interfering effects of hydrolytic polymerization of iron(III) on the saturation of apotransferrin in serum and on the colorimetric determination of the unbound iron excess at pH 8.3, conditions have been studied for the preparation of the iron-nitrilotriacetate-complex (Fe(NTA)2) solution at pH 8.3 with respect to its reactivity with the reductant sodium ascorbate and with the chromogen bathophenanthroline-disulfonate in photometric standards and in samples containing iron-saturated serum. The validity of the results for the UIBC thus obtained has been investigated (1) by direct spectrophotometric titration with Fe(NTA)2 of the apotransferrin in serum by measuring the absorbance of transferrin at 470 nm in 50-mm cuvettes, and of the UIBC using the modified indirect iron saturation excess assay, both of which gave the same saturation points, and (2) by the correlation of the TIBC obtained from serum iron determinations and the UIBC, with the transferrin concentration measured by the radial immunodiffusion assay. Results of UIBC determinations are presented along with serum iron concentration, TIBC, and transferrin saturation in groups of subjects with normal iron stores and prelatent, latent, and manifest iron deficiency.

Anemia, Hypochromic↗
PubMed1983

Pancreatic and salivary amylase determination using a short-chain chromogenic substrate (alpha-4-nitrophenyl-maltoheptaoside) and an amylase inhibitor.

We describe a simple method to determine serum amylase isoenzyme activity with alpha-4-nitrophenyl-maltoheptaoside as substrate and the use of an amylase inhibitor. Day-to-day reproducibility (CV) was 2% for total amylase, 3-5% for pancreatic and salivary amylase; within-day precision was 1% for total amylase, 1-4% for pancreatic and salivary amylase. The concentrations of total, pancreatic and salivary amylase were determined in 169 sera obtained from healthy adults (82 men and 87 women). Total, pancreatic and salivary amylase concentrations in males were respectively 184, 105 and 66; in females 210, 97 and 92 U/l (mean). Our method is simple and rapid; our results agree well with those of other authors, who have used electrophoretic or blue starch methods.

Adult↗
PubMed1984

A colorimetric assay for plasma antithrombin III using a new synthetic peptide substrate (PS-915).

A colorimetric assay for plasma antithrombin III (ATIII) has been developed, using a new synthetic peptide substrate, PS-915 (H-D-Phe-Pro-Arg-CHA). PS-915 is freely water-soluble and its aqueous solution is stable. It is highly specific for thrombin and its Km value is about the same as that of S-2238. By enzyme hydrolysis, the new substrate liberates 3-carboxy-4-hydroxyaniline (CHA), which turns blue in color due to the complex formation with added alkaline-pentacyanoammine ferroate. The assay is a three-stage kinetic, one-point procedure, based on the method of antithrombin (heparin cofactor activity) determination. Since absorption measurements of the CHA are usually obtained at 700 nm, no blank correction is necessary even when hyperbilirubinemic, lipemic and/or hemolyzed plasma are used. The calibration curve for ATIII is linear over the range of 0-175% of normal and has a high degree of reproducibility. The results obtained by this method are well correlated with data obtained by the commonly used chromogenic assay or by radial immunodiffusion.

Adult↗
PubMed1985

A new chromogenic endotoxin-specific assay using recombined limulus coagulation enzymes and its clinical applications.

A conventional limulus test is not specific to endotoxin because of the presence in amebocyte lysate of a (1----3)-beta-D-glucan-sensitive factor. By fractionating coagulation enzymes in the lysate and recombining only those factors involved in endotoxin-induced coagulation, we have developed a new test specific to endotoxin. The recombined enzymes reacted only with endotoxin, and not with fungal polysaccharides. Conventional amebocyte lysate, on the other hand, reacted with both of them. A good linearity was obtained with this method between endotoxin concentration and absorbance with a sensitivity of 1 pg/ml of Escherichia coli 0111:B4 endotoxin. The regression lines for different types of endotoxins were parallel to one another. For the correct diagnosis of endotoxemia, this new test has a definite advantage over the one using whole amebocyte lysate.

Arthropod Proteins↗
PubMed1987

A simple chromogenic assay for arylsulfatase A.

Arylsulfatase A hydrolyzes the artificial chromogenic substrate 4-nitrocatechol-sulfate at 0 degree C at a rate of 24% of that at 37 degrees C whereas arylsulfatase B is almost inactive at 0 degree C. Based on this observation, a simple assay was developed which permits the accurate determination of low residual arylsulfatase A activities in cultured skin fibroblasts of infantile, juvenile and adult MLD patients and pseudodeficient individuals. In cultured skin fibroblasts, the following residual activities were found with this assay system: late-infantile patients, 0.0%, one juvenile patient, 1.0%, adult patients, 4.4-14% of normal average. healthy pseudodeficient probands ranged between 18% and 32%.

Catechols↗
PubMed1987

Analytical and clinical evaluation of commercial protein C assays.

Protein C deficiency is an important risk factor for thrombosis. Recently several commercial assays for this protein have become available. We evaluated two antigen and three activity assays in 50 healthy volunteers, 52 patients with deep venous thrombosis (DVT) proven by positive impedance plethysmography (IPG) and flebography, and 48 control patients referred to us for objective diagnosis of DVT but with repeatedly negative IPG. All subjects were less than 50 yr of age. Based upon assay performance, correlation of the assays, influence of heparin, and practical ease, an ELISA antigen assay and a chromogenic activity assay are recommended. The prevalence of protein C deficiency cannot be accurately determined from this study, because 3 DVT negative and 13 DVT positive patients were receiving coumarin therapy. However, based upon protein C:factor II antigen ratios, at least 7 of the DVT positive patients are likely to be protein C-deficient. Protein C determination should, therefore, be considered in all DVT patients less than 50 yr of age.

Chromogenic Compounds↗
PubMed1987

Spectrophotometric assay of xanthine oxidase with 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphonate) (ABTS) as chromogen.

A new method for the determination of xanthine oxidase activity, based on the oxidation of 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphonate) (ABTS) by use of uricase and peroxidase, is described. The absorbance increase of the oxidized form of ABTS, measured after 10 min at 410 nm is proportional to xanthine oxidase activity. The method is sensitive, precise (CV below 8.3%), and linear up to 20 U/l. The analytical recovery of the ABTS-method was quantitative. Comparison with the UV and colorimetric NBT-method gave good correlation (r greater than or equal to 0.984). Reference values for serum xanthine oxidase activities determined with the new ABTS-method on 83 healthy persons are 0 to 1.20 U/l.

Adolescent↗