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Y Lifshitz

Publications and source records attributed to Y Lifshitz.

28 records · Page 2Linked to original sources
PubMed1986

Structure-activity relationships in the mutagenicity of N-substituted derivatives of phenanthrene-9,10-imine.

A series of K-region, N-substituted phenanthrene imines were tested for mutagenicity in Salmonella typhimurium TA100. All chemicals were mutagenic in the absence of an exogenous metabolic activation system. The apparent decay times of the mutagenic species in diffusion plates and their alkylating activities were also measured. The unsubstituted phenanthrene-9,10-imine was approximately 70-fold more mutagenic than the corresponding phenanthrene-9,10-oxide. N-substitution with electron-releasing groups resulted in chemicals that were more mutagenic than those substituted with electron-withdrawing groups. The mutagenic activity of the latter group of chemicals was comparable with that of phenanthrene-9,10-oxide. Except for N-chlorophenanthrene imine, both alkylation of p-nitrothiophenol and apparent decay times in diffusion plates were inversely correlated with mutagenicity. It is hypothesized that reactivity towards p-nitrothiophenol (alkylating activity) and mutagenicity reflect different reactions, in contrast to other chemical mutagens. The results suggest that the high potency of phenanthrene imines as mutagens is possibly due to DNA binding via an aziridinium ion rather than a carbonium ion.

Alkylating Agents↗
PubMed1981

Modulation by divalent metal ions of the autocatalytic reactivity of adenosinetriphosphatase from chloroplasts.

A nonlinear, pre-steady-state initial rate of ATP hydrolysis is obtained on the addition of a divalent metal ion--ATP complex to a heat-activated coupling factor 1 isolated from chloroplasts. The acceleration of the initial rate follows first-order kinetics. The observed first-order kinetic constant (kobsd) changes with the concentration of the substrate, reaching half-maximal value at the Km for ATP hydrolysis. Preincubation of the enzyme with divalent metal ions decreases the kobsd from 1 to 0.04 s-1. Saturation of the divalent metal ion effect was obtained at the micromolar range. It is suggested that the autocatalysis is a result of early stages in ATP hydrolysis which induce conformational changes in the enzyme. Binding of divalent metal ions in the absence of ATP slows down this change.

Adenosine Triphosphatases↗
PubMed1981

Dexamethasone for prevention of respiratory distress syndrome: multiple perinatal factors.

Antepartum dexamethasone administration was associated with a significant lowering of the incidence of respiratory distress syndrome (RDS) and with marked reduction of early neonatal mortality in premature infants. Dexamethasone had its greatest effect in infants delivered between 28 and 32 weeks' gestation (P < .001), and the difference was still significant up to 34 weeks' gestation (P < .05). Although the effect of dexamethasone was more marked in patients with intact membranes, it was also effective in those with prolonged rupture of the membranes. Membrane condition before delivery was unrelated to the incidence of RDS. The effectiveness of dexamethasone was analyzed with respect to the condition of the infant at delivery, the mode of delivery, and multiple births. As compared to the controls, dexamethasone was most effective in singletons, infants delivered vaginally, and those with high Apgar scores. The effect of dexamethasone was not significant in twins, breech deliveries, cesarean section deliveries, or infants with low Apgar scores. The effects of dexamethasone appear to be modified by intrauterine asphyxia. Dexamethasone therapy cannot be substituted for optimal delivery conditions of the premature.

Dexamethasone↗
PubMed1979

Delivery at 40 years of age and over.

This is a retrospective review of 494 deliveries during a 10-year period in women aged 40 or more years. A decline in the incidence of deliveries in this age group was noted, from 2.1% in 1965 to 1.2% in 1974. An increased frequency of complications during pregnancy and delivery, a high rate of cesarean sections, and increased perinatal mortality rate, and more congenital malformations were recorded as compared with both a control group of randomly selected grand multiparas and a general obstetric population group of patients under the age of 40 years. The fetal outcome improved during the last years of the study; the perinatal mortality rate dropped from 10.4% in 1965 to 1.6% in 1973 to 0% in 1974. This achievement reflects the significant progress in obstetrics that has been made during these years.

Adult↗
PubMed1975

Control of proton translocation induced by ATPase activity in chloroplasts.

1. Proton uptake was induced by ATP in the dark following light triggering of ATPase activity in chloroplasts. The accumulated protons were released when ATPase activity was inhibited by the energy transfer inhibitor DIO-9. 2. Approximately two protons were taken up for each ATP hydrolyzed at pH 8. A drop in H+/ATP ratio was caused by uncouplers such as NH4Cl and carbonyl cyanide p-trifluoromethoxyphenylhydrazone. These uncouplers caused an increase in the rate of ATP hydrolysis without a corresponding increase in proton uptake. 3. The energy transfer inhibitor dicyclocarbodiimide inhibited both ATPase activity and the rate of proton uptake without changing the H+/ATP ratio. 4. The antibiotic valinomycin caused an increase in the rate of both proton uptake and ATP hydrolysis without altering the ratio of H+/ATP. The H+/ATP ratio varied with changes in the external pH. The results were discussed in view of the chemiosmotic theory of oxidative and photosynthetic phosphorylation.

Adenosine Triphosphatases↗