Low Tryptophan Concentrations Research Articles

Absence of hyperchromic effect in DNA heated above Tm., in the presence of tryptophan.

A strong interaction between DNA and Tryptophan in water solutions is described. This interaction determines the absence of hyperchromic effect in heated DNA above its melting point, when Tryptophan is present (base mol/tryptophan mol). At lower concentrations of Tryptophan only a shift of the Tm. of the DNA-Tryptophan solutions and a change in the shape of the thermal denaturation curves occurs. These effects are neither due to the ionic strength of the Tryptophan. nor to pH variations. P.M.R. spectroscopic studies confirm the interaction of the uracil ring of Uridine and the indol ring of Tryptophan.

Anthranilate synthetase and the allosteric protein model.

Summary 1. A hypothesis is proposed to account for the observation that o-dihydric phenol synthesis by whole cells of the tryptophan auxotroph Aerobacter aerogenes NC3 is completely inhibited by low concentrations of tryptophan added to the substrates. It is claimed that in this strain a mutation has resulted in a defective anthranilate synthetase, such that the “active site” is changed, altering the enzymic function, but retaining allosteric inhibition by tryptophan. 2. In sustaining this hypothesis, previously unpublished results, evidence from a number of published sources arid work with Saccharomyces cerevisiae and Neurospora crassa, is considered in relation to (a) the original observations, (b) the normal enzymic site of feedback inhibition by tryptophan and (c) the nature of anthranilate synthetase. 3. As a result of considering various models for anthranilate synthetase in Aerobacter aerogenes and the inter-relationship between this activity and other tryptophan-path enzymic functions in Saccharomyces cerevisiae and Neurospora crassa, an allosteric aggregate enzyme model is proposed. It accounts for the genetic, nutritional and biochemical data. 4. Potential consequences of the aggregation of enzymic functions into alrosteric protein complexes are discussed and, in particular, an extension of the present concept of the function of allosteric proteins in biological systems.

Essential amino acids in microorganisms.

The cells of 19 species of bacteria, actinomyces, and yeasts were analyzed for protein and essential amino acids. A rapid quantitative method for amino acid determination using one-dimensional paper chromatography was developed. The cellular protein from all species contained relatively high concentrations of lysine, somewhat lower concentrations of tryptophan and threonine, and very low concentrations of methionine. All of the 10 essential amino acids were found in each species tested, although individual differences in the relative and absolute amounts were observed.

The Essential Amino Acid Content of the Proteins Isolated from Milk of the Cow, Ewe, Sow, and Mare

Summary Mixed proteins isolated from the milk of the cow, ewe, sow, and mare have been assayed for the essential amino acids by microbiological methods. In general, the concentration of the amino acids in the proteins from the different species is similar, although higher concentrations of arginine and lower concentrations of tryptophan may be present in the milk proteins of the sow and mare than are present in the proteins of the cow and ewe. There appeared to be no difference between the amino acid content of the proteins isolated from the milk of the Shropshire, Rambouillet, and Hampshire breeds of ewes. Species difference in the amino acid components of mammalian milk proteins is not as spectacular as it is in the fatty acids components of milk fat, although the protein molecules are more complex than fat molecules.