Effect of an exogenous energy source and amino acids on DNA synthesis in regenerating rat liver

Rats on a protein-free diet synthesized less DNA after partial hepatectomy than rats on a normal diet. In regenerating livers of animals on the protein-free diet, induction of several enzymes involved in the DNA precursor synthetic pathway, and especially ribonucleotide reductase, were depressed. When young rats were maintained solely by parenteral nutrition after partial hepatectomy, exogenous amino acids were more important than the exogenous energy source for induction of enzymes involved in synthesis of DNA and its pyrimidine nucleotide precursors. In particular, induction of ribonucleotide reductase appeared to be controlled by exogenous amino acids. Tryptophan, methionine, phenylalanine, leucine, valine, isoleucine and threonine seemed to stimulate the induction of this enzyme most after partial hepatectomy.     

Metabolic activation of a mutagen, 2-amino-6-methyldipyrido-[1,2-a:3′,2′-d]imidazole. Identification of 2-hydroxyamino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole and its reaction with DNA

A potent mutagen, 2-amino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole(Glu-P-1), isolated from pyrolysates of L-glutamic acid and casein, was metabolically activated and bound to DNA. An activated form was identified as 2-hydroxyamino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole(N-OH-Glu-P-1). Synthetic N-OH-Glu-P-1 reacted with DNA only after O-acetylation to give a modified DNA, which on hydrolysis gave 2-(C⁸-guanyl)amino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole(gua-Glu-P-1). The same adduct was isolated from DNA modified with Glu-P-1 by microsomes in vitro, as reported earlier.     

Spinach chloroplasts scavenge hydrogen peroxide on illumination

Intact spinach chloroplasts isolated by the modified silicasol density centrifugation scavenged H₂O₂ on illumination ata rate about 3-fold that of bicarbonate-dependent O₂-evolution.Accompanying the disappearance of 1 mole of H₂O₂ is the evolutionof a half mole of O₂. The photoscavenging of H₂O₂ was inhibitedby 3(3,4-dichloro-phenyl)-l, l-dimethylurea, cyanide and azide.These results indicate that in chloroplasts H₂O₂ is reducedto H₂O by a cyanide and azide-sensitive peroxidase using a photoreductantas an electron donor. (Received July 4, 1980; )     

24,24-Difluoro-25-hydroxyvitamin D3-enhanced bone mineralization in rats. Comparison with 25-hydroxyvitamin3 and vitamin D3

The biological activity of 24,24-difluoro-25-hydroxyvitamin D₃ was assessed using elevation of serum phosphorus and healing of rickets of vitamin D-deficient rats. Various levels of 24,24-difluoro-25-hydroxyvitamin D₃ and 25-hydroxyvitamin D₃ were administered daily for 2 weeks in the dose range of 6.5 to 3250 pmol after feeding rats a low phosphorus, vitamin D-deficient diet for 3 weeks. Vitamin D₃ was concurrently tested at dose levels of 650 and 3250 pmol. 24,24-Difluoro-25-hydroxyvitamin D₃ is approximately equipotent with 25-hydroxyvitamin D₃ in stimulation of growth, mineralization of rachitic bone, and elevation of serum inorganic phosphorus. Radiological manifestations of rickets were also equally improved by 24,24-difluoro-25-hydroxyvitamin D₃ and 25-hydroxyvitamin D₃. Compared with vitamin D₃, these compounds were approximately 5 to 10 times more active in mineralization using rats on a low phosphorus, vitamin D-deficient diet. The functional role, if any, for 24-hydroxylated vitamin D compounds, such as 24,25-dihydroxyvitamin D₃, therefore remains obscure. It appears that vitamin D compounds that cannot be 24-hydroxylated evoke no disorder in bone mineralization.     

Metabolic Requirements for the Development of Hemadsorption Activity and Virus Formation in BHK-21 Cells Infected with Newcastle Disease Virus

Differential effect of various metabolic inhibitors on the development of hemadsorption activity and virus formation in cells infected with Newcastle disease virus (NDV) was investigated. It was found that, in BHK-21 cells infected with NDV, cycloheximide did not prevent the development of hemadsorption activity, whereas protein synthesis and virus formation by the cell were rapidly inhibited by the drug. When the drug was added to the culture at 4.5 h after infection or later, hemadsorption activity of the cell continued to develop normally for about 1 h. Similar increase in hemadsorption activity was found in cells which were treated with anti-NDV serum (to neutralize their hemadsorption activity) and then washed and incubated with cycloheximide. However, when cells were treated with the drug early in the infection (1.5 or 3.0 h), they did not show any detectable hemadsorption reaction throughout the infection. In contrast to cycloheximide, iodoacetate added to the culture together with sodium azide inhibited completely both the development of hemadsorption activity and the formation of progeny virus. These results suggest that the change of cell surface to become hemadsorptive may depend upon the energy generating system but not upon de novo synthesis of protein, whereas production of infectious virus may require continuous synthesis of protein.     

Production of Phosphatase by Aspergillus awamori var. kawachii in a Low Phosphate Medium

The effect of phosphate on the production of phosphatases by Aspergillus awamori var. kawachii was studied. In a high phosphate medium, little phosphatase was produced, and the phosphatase activity was predominately for beta-glycerophosphate. In a low phosphate medium, the production of phosphatase was increased and activity for glucose-6-phosphate predominated. Medium containing 1 mg of phosphorus per 100 ml was optimal, and the amount of phosphatase produced in this medium was about 200 times that produced in a high phosphate medium. By means of column chromatography on diethylaminoethyl cellulose, the phosphatase produced in the high phosphate medium was found to be eluted mainly at fraction e; the phosphatase of the low phosphate medium was separated into fractions a, b, c, and d. Thus, the phosphatase fractions produced in the low phosphate medium were different from those of the high phosphate medium. Since no specific effect on the production of esterases was observed when various phosphate esters were used as substrates, the enzymes of phosphate metabolism appear to be activated by nonspecific phosphate sources.