Carl Niemann

The consequences of systematic error in enzyme kinetics

Abstract The consequences of systematic error in enzyme kinetics was considered by introducing a first order error term into the Michaelis-Menten-Briggs-Haldane equation. The situations investigated were those involving over- or undercorrection of an enzyme or substrate blank reaction in the absence and presence of product inhibition and in the presence of a totally competitive, non-competitive or uncompetitive inhibitor. In addition, consideration was given to errors arising from a departure from the Beer-Lambert relationship and those proportional to the velocity or substrate concentration. Finally, attention has been called to the questionable validity of using weighting procedures to correct for random error in the presence of systematic error.

Further observations on the behavior of carbohydrates in seventy-nine per cent sulfuric acid☆

Abstract The spectral properties of heated 79% sulfuric acid solutions of a number of representative polysaccharides have been determined and the use of these data for analytical purposes has been discussed. The question of interference by proteins and nucleic acids has been considered.

Nitrogen analogs of representative substrates and inhibitors of α-chymotrypsin

Abstract The replacement of the α-methine or α-methylene group, present in a series of representative substrates and inhibitors of α-chymotrypsin, by a nitrogen atom or an amino group leads to a loss of substrate activity or to an increase in the magnitude of the enzyme-inhibitor dissociation constants. An explanation of these phenomena is proposed.

The interaction of α-chymotrypsin with 1-acyl-2-(α-aminoacyl)hydrazines

Abstract 1-Acetyl-2-( L -tyrosyl)hydrazine is a particularly effective inhibitor of α-chymotrypsin. The principal obligatory structural requirements for inhibitors of this type have been determined and the nature of their interaction with the enzyme has been examined.

The effect of calcium chloride on several α-chymotrypsin-catalyzed hydrolyses

Abstract The extent to which the reactivity of systems containing α-chymotrypsin and specific substrates of this enzyme may be enhanced by the presence of calcium chloride has been shown to be dependent not only upon the concentration of this salt but also upon the nature and/or concentration of several buffer components. An additional dependence upon the nature of the specific substrate has not been excluded.

The interaction of α-chymotrypsin with α-N-acetyl-l-phenylalaninamidoxime

Abstract α-N-acetyl- l -phenylalaninamidoxime, i.e. , l -α-acetamido-β-phenylpropionamidoxine, although capable of combining with the catalytically active site of α-chymotrypsin is not hydrolyzed by this enzyme under conditions where the corresponding amide and hydroxamide will function as substrates.

A dilatometric investigation of the α-chymotrypsin—catalyzed hydrolysis of nicotinyl-l-tryptophanamide

Abstract A novel dilatometer was developed which eliminates all joints, stopcocks, and openings directly in contact with, or in the path of, reactants and reaction mixtures. Observation of volume changes occurring during hydrolytic reaction permitted calculation of the extent of hydrolysis per unit time. Kinetic constants obtained by dilatometric procedures agreed well with those determined by other means. The dilatometric method described herein shows promise as an alternate way in which to evaluate kinetic constants, and should provide a valuable means of data validation.

Toxic protein degradation products.

Summary Toxic polypeptides, similar to those obtained by Vaughan(1), have been prepared by treatment of certain proteins with boiling 2% ethanolic sodium hydroxide. These substances are soluble in water and in ethanol, are capable of dialyzing through a cellophane membrane and have been shown to be a mixture of essentially basic polypeptides of similar composition. Their characteristic absorption at 270–280 mμ does not appear to be related to their toxic properties. At an amino acid level the polypeptides differ from their parent proteins in that they contain little or no cystine, serine or threonine. The most toxic preparations, obtained by a salting out procedure, followed by dialysis or by ion exchange chromatography, while nontoxic when given orally were lethal to guinea pigs at a level of 0.5 mg/kg intravenously. Pretreatment of the animals with atropine, epinephrine or Neo-Antergan failed to prevent or modify the effect of a lethal dose of the polypeptide thus excluding liberation of histamine or acetylcholine as the principal cause of toxicity.