Harold H. Williams

Lipide phosphorus and cholesterol changes in the hen's egg during incubation.

Abstract Lecithin phosphorus, cephalin phosphorus, total lipide choline, and free cholesterol gradually decrease in the residual yolk with incubation, whereas these substances simultaneously show a gradual increase in the embryo. There is also a progressive increase in esterified cholesterol in both yolk and embryo. The hens egg contains practically no sphingomyelin, but some sphingomyelin appears to be formed by the embryo during development. Phospholipide and cholesterol metabolism reach their peak between the 18th and 21st days of incubation. The percentage tissue concentration of lipide phosphorus and free cholesterol remains relatively constant in the residual yolk, but decreases in the embryo during incubation.

The enhancement of selenite toxicity by methionine in Escherichia coli.

Abstract The toxicity of SeO 3 −− to wild type Escherichia coli is enhanced by the presence of l -methionine in the growth medium. Data are presented which show that the same degree of toxicity is exhibited by the methionine-requiring mutant of E. coli , A.T.C.C. 9663. d -Methionine is shown to be ineffective. Exogenous methionine suppresses the biosynthesis of selenomethionine as well as methionine. The suppression of selenomethionine biosynthesis provides a basis for the enhanced toxicity of SeO 3 −− . It is also possible that the biosynthesis of selenocyst(e) ine may account for part of the enhanced toxicity. Interaction between SeO 3 −− and methionine as a basis for enhanced toxicity is unlikely from the data obtained on the methionine-requiring mutant, A.T.C.C. 9663.

Transaminase studies in germinating seeds.

Abstract The changes in glutamic-alanine and glutamic-aspartic transaminase during the germinating period of the seedling have been studied with plants from three plant families. It was found that in the germinating seed embryo the glutamic-aspartic transaminase activity was in general higher than the glutamic-alanine transaminase activity. At the beginning of germination all plants studied contained approximately the same amount of transaminase: i.e., about 5–10 units/embryo. However after 120 hr. of germination there were wide variations in the amount of transaminase found in the different species. In most of the plants studied the transaminase activity/mg. protein nitrogen revealed a proportionally greater increase in the enzymatic activity than that of the protein nitrogen. Stimulation of growth and metabolism of the embryo by the use of a mineral supplement for germination of the seeds produced an increase in the rate of formation of both transaminase and protein nitrogen. However, the production of the enzyme was relatively greater than the formation of protein nitrogen. The results indicated that no definite relationships existed between the changes in glutamic-alanine or glutamic-aspartic transaminase activity and the formation of protein. This would suggest that in plants, protein synthesis is not a direct function of transaminase activity; it may play an indirect role in protein synthesis by its action on the interconversion of amino and keto acids.

A comparison of selenite and tellurite toxicity in Escherichia coli

l -Methionine enhances the toxicity of TeO3− and SeO3− to E. coli wild type. d -Methionine is ineffective. Similar effects are obtained with the methionine-requiring mutant A.T.C.C. 9663. The enhancement of TeO3− toxicity can be produced by a wide variety of sulfur compounds. Such compounds include those which serve as complete or partial sources of sulfur for E. coli in addition to those not metabolized by the organism. All effective compounds contain sulfur in its most reduced state (S−). SeO3tt- does not show this effect. The enhancement of TeO3− toxicity in contrast to SeO3− by more diverse sulfur compounds demonstrates that a sulfur-TeO3− interaction takes place which has an effect on E. coli that is not comparable to any SeO3−-sulfur interaction.

D-Amino Acids as Source of Non-Specific Nitrogen for Growth of Rats

Summary Rats fed a diet containing physiological amounts of essential L-amino acids but lacking non-essential amino acids grew at a slow rate. Growth rate was increased by increasing concentration of all essential amino acids. Feeding a mixture of DL-amino acids in comparable amounts resulted in growth retardation of animals. Growth inhibition produced by the racemic mixture was traced to an isoleucine deficiency resulting from inclusion of DL-isoleucine, which was actually a mixture of all 4 isomers, thus effectively diluting the active isomer. Substitution of L-isoleucine or a mixture of L- and D allo-isoleucine for the racemic compound in the DL mixture entirely overcame inhibition and produced growth comparable to that obtained with L-amino acids. The experiments provide evidence that D-amino acids can be effectively used as source of nitrogen for biosynthesis of non-essential amino acids.

Quantitative studies on selenite metabolism in Escherichia coli.

Abstract Selenite metabolism in Escherichia coli has been observed to involve at least two phases. One phase represents the reduction of selenite to elemental selenium. A second phase represents the incorporation of selenium into organic molecular structure (selenomethionine, etc.). Although elemental selenium is soluble in CS 2 , it was found that the solvent would not completely extract Se from the cells. Complete extraction was possible only after enzymic hydrolysis of the protein material, an indication that part of the elemental selenium was tightly bound to the protein. It was observed that although selenite reduction depended upon cell growth, it was not directly correlated to cell density. Continuous culture of cells in selenite media led to increased selenite reduction but with a decrease in cell population. Furthermore, it was found that normal cell suspensions, when incubated in selenite buffer, were capable of reducing selenite, thus indicating the presence of a reductase system in the normal cells. However, preliminary attempts to show the reductase activity in a cell free preparation were unsuccessful.

The effects of selenite on β-galactosidase induction in Escherichia coli

Abstract Toxicity of selenite to Escherichia coli ML-30 is enhanced if the organism is inoculated into a selenite medium which contains lactose as the only carbon source. In media of this type, the cells must synthesize β-galactosidase before growth can take place, and a lag period is produced which is proportional to the selenite concentration. This phenomenon is not observed when another carbon source such as succinate is present, or, if the cells are fully induced for β-galactosidase. Isotope uptake studies demonstrate that the above phenomenon is not the result of a permeability barrier produced by selenite. The data suggest that the opposite is true and permeability to the inducer, lactose, is increased by selenite. The rate of β-galactosidase biosynthesis is increased in selenite supplemented media using lactose, or melibiose as the inducers, and succinate, maltose, glycerol, or lactic acid as carbon sources. By use of differential rate plots, the biosynthesis rate constants were evaluated and found to be greater than the controls which contain no selenite. The inhibition of β-galactosidase by selenite was studied and found to occur only at concentrations higher than those employed in the studies described above. Two explanations are offered for the results described herein. It is postulated that selenite uncouples growth from cell division. This would allow an increase in bacterial protein without cell division and give the net effect of an increased enzyme biosynthesis rate. Another possibility is that β-galactosidase is synthesized at a faster rate since it contains more methionine than the other cell protein. Thus, it is a potential depository for selenomethionine which is the product of selenite detoxification.

The availability of leucine derivatives for growth of rats

Abstract A number of synthetic derivatives of the essential amino acid leucine were tested for biological activity using the growth of rats as the main criterion. Of these, glycyl- l -leucine, acetyl- l -leucine, l -leucine ethyl ester, and l -leucine methyl ester supported growth while caproic acid, phthaloyl- l -leucine, benzoyl- dl -leucine, and carbobenzoxy- l -leucine were found to be inactive. Chloroacetyl- l -leucine actually suppressed growth to a greater degree than a leucine-deficient diet. The N-methyl derivative of leucine was only slightly active. Comparison of the N-acetyl derivatives of l - and dl -leucines indicates that N-acetyl- d -leucine is devoid of any activity.