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K Lorentz

Publications and source records attributed to K Lorentz.

At least 37 records · Page 2Linked to original sources
PubMed1979

Studies on isoamyalse formation in biological fluids.

Storage of human serum, saliva and duodenal secretion transformed amylase fractions on cellulose acetate membranes into more anionic forms. Incubation with lectins, proteases, glucosidases, neuraminidase and some effectors did not modify this conversion, which was promoted by rising temperature and pH values. Increasing concentrations of ammonium ions delayed the transformation of amylolytic fractions, thus indicating nonenzymatic deamidation as the reason for isoamylase development. A change of molecular weight could be excluded.

Amylases↗
PubMed1979

alpha-Amylase assay: current state and future development.

alpha-Amylase can be measured continuously with the aid of 4-nitrophenyl glucosides, especially 4-nitrophenyl maltotrioside; the large scale enzymatic synthesis of this compound seems to be possible. Another method, which does not suffer from interference by endogenous glucose, consists of the hydrolysis of maltotetraose by alpha-amylase, followed by the determination of maltose. The substrate and the auxiliary enzymes are, however, relatively expensive. Continous methods, based on the measurement of the glucose released by alpha-amylase, are more sensitive. However, they suffer from interference by blood sugar, with exception of mechanized procedures, which remove glucose by gel filtration of the sample. Moreover these methods need alpha-glucosidase, which degrades maltooligosaccharides consisting of less than seven glucose units, whereas higher polymerized substrates show slower degradation rates by amylase, and the kinetics are not easy to understand.

Amylases↗
PubMed1979

Arylesterase in serum: elaboration and clinical application of a fixed-incubation method.

A sensitive, specific, and simple method for determining serum or urine arylesterase (EC 3.1.1.2) is described. The enzyme acts on phenyl acetate to release phenol, which produces a stable indophenol dye with 4-aminoantipyrine and potassium ferricyanide. Arylesterase, a thiol enzyme, is reactivated by 2-mercaptoethanol and by cysteine, but not by reduced glutathione. Calcium is indispensable to stabilize and to activate (Km = 0.85 mmol/L) the enzyme; complete protection is achieved at CaCl2 20 mmol/L. Magnesium acts as a weak (Ki = 116 mmol/L), lanthanum as a potent (Ki = 5 mumol/L) competitive inhibitor. The activity is measured in diluted sera at phenyl acetate 4.0 mmol/L (Km = 1.12 mmol/L), pH 7.8 and 25 degrees C. The normal range extends from 53 to 186 kU/L, and four isoenzymes are present in sera from healthy adults. Arylesterase decreases in hepatic disorders, especially in cirrhosis and carcinoma of the liver, with reduction of the penultimate fraction in polyacryalmide gel electrophoresis.

Adolescent↗
PubMed1979

[Lectins as reagents for the differentiation of serum enzymes. Lectins as reagents, I. (author's transl)].

Lectins from Canavalia ensiformis, Phaseolus vulgaris, and Triticum vulgare react with arylamidase, alkaline phosphatase, gamma-glutamyltransferase, and cholinesterase of human sera by formation of enzymatically active, mostly insoluble complexes. Arylamidase, alkaline phosphatase, and cholinesterase react more intensely in sera of healthy people than in sera of patients with liver and neoplastic diseases. Arylesterase is bound to a distinct degree only by concanavalin A. The enzymes mentioned above also react slightly with the following lectins in order of decreasing intensity: Ricinus communis, Arachis hypogaea, Helix pomatia, Glycine max, Dolichos biflorus, and Ulex europaeus. Though multiple forms containing less sialic acid are favourably bound, preincubation with neuraminidase does not improve the reaction except with soybean lectin. Since higher concentrations of lectins react also with fast moving fractions of high sialic acid content, no steric hindrance of the binding between lectins and sialoenzymes is supposed, as concluded from determination of the total enzyme activity.

Alkaline Phosphatase↗
PubMed1977

[A new method for the preparation of linear polyacrylamide gradients (author's transl)].

Continuous linear gradients improve electrophoretic separations in polyacrylamide. They are obtained by overlayering equal volumes of two monomer solutions with different acrylamide concentrations, namely 180-260 and 23-50 g/l, in the usual gel tubes. The tubes are tilted 3-10 degrees to the horizontal, and rotated around their longitudinal axis until the parts of both solutions in contact are mixed homogeneously. Subsequent polymerization takes place in the vertical position. The more concentrated lower solution contains 4-nitrophenol, so that the final polymer concentration at any point of the gel can be measured densitometrically. The construction and handling of the rotation device are simple and yield highly reproducible results. This versatile method was evaluated for the separation of proteins, lipoproteins, and enzymes in human serum and yields 27-30 protein fractions by additional use of a pH-gradient.

Blood Protein Electrophoresis↗
PubMed1975

A new method for the assay of aminoacylase: elaboration of a fixed-incubation method for routine measurements.

A simple method suitable for routine determinations of aminoacylase (EC 3.5.1.14) in serum and tissue homogenates is described. It is based on the formation of red charge-transfer complexes from p-benzoquinone and amino acids liberated by cleavage of acylamino acids. Optimal substrates are trifluoroacetyl-L-methionine and chloroacetyl-L-methionine, the first being rapidly hydrolyzed by pancreatic tissue, the latter by liver and kidney homogenates. Sera preferentially split the chloroacetyl compound. Optimal conditions for the assay of serum activity are: 18-20 mm9l/l substrate concentration, 50 mmol/l phosphate buffer pH 6.0, no additives.

Amidohydrolases↗
PubMed1975

Clinical application of a new method for the determination of aminoacylase in human serum.

Serum aminoacylase was assayed in 242 patients with various internal disases. The enzyme activity was normal in 89 cases without hepatic involvement and above normal in all forms of liver disease, the highest values being seen in acute viral hepatitis. Obstructive liver disease and hepatic carcinoma likewise caused a distinct enzyme increase, but this elevation was referred to secondary liver damage as in cases of congestive heart failure. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and aminoacylase activities were closely correlated, and aminoacylase is regarded as a sensitive and specific indicator of hepatic affections.

Alanine Transaminase↗
PubMed1975

Studies on aryl phosphate hydrolysis by human acid phsophatases.

Acid phosphatases from human tissues were investigated with respect to the cleavage of six different aryl phosphates. The enzymes, except the prostatic one, showed increasing Km values with increasing substrate concentrations at a constant pH. Electrophilic substitution of the aromatic ring lowered the reaction velocity, but apparently did not change the Km. The optimum hydrolysis was at pH 3.0--6.0 without any regular pattern, which could depend on the substrate configuration.

Acid Phosphatase↗