Effect of oxygen on growth of cultured myocardial cells

The present study was designed to explore the effects of environmental oxygen as a possible regulator of cardiac cell division and growth. Trypsindispersed heart cells from the ventricles of chick embryos 8 to 12 days old were grown in culture at 37°C in a nutrient medium (NCI) with 10% fetal calf serum. They were exposed to constant 5% CO 2 gas environments in which the percent of O 2 was varied. Net protein synthesis increased progressively as O 2 was reduced from 80% to 2 to 5%. After the first 24 hours, little further protein synthesis occurred in plates grown in 80% O 2 . The rates of cellular incorporation of 14 C-amino acids and uridine-2- 14 C increased progressively as the fraction of O 2 was reduced. In cells grown at 80% O 2 , incorporation of uridine-2- 14 C into RNA was impaired before that of 14 C-amino acid into protein. After actinomycin-D (5 µg/ml) (which quickly halted uridine incorporation into the rapidly labeled fraction of RNA), the rate of incorporation of 14 C-amino acid into protein declined exponentially. This allowed for calculation of the half-life of messenger RNA (mRNA), which was the same for cells grown at 80% O 2 as for cells grown at 20% O 2 ; increased degradation of mRNA at higher P o 2 is thus ruled out. Decreased O 2 tension results in increased rates of cell division and protein synthesis in vitro. The molecular site of action appears to be at or before RNA readout from DNA.

[Physical and biological half-life of radiochemically pure 59Fe]

At delivery commercial 59Fe-preparations contain up to 1% contamination by 60Co, 65Zn, 54Mn, 46Sc, 134Cs, etc., so that the physical half-life of such preparations is not constant and starts to increase permanently after about 100 days. Anion exchange chromatography was used to prepare 59Fe with a radiochemical purity of ≧ 99.999999% as demonstrated by analytical anion exchange chromatography, paper- and thin-layer chromatography, and γ-spectroscopy. The physical half-life of radiochemically pure 59Fe was found to be constant over 500 days with 44.52 ± 0.016 days (λ= 0.015568 ± 0.0000056 [d-1]).

The whole-body retention of radiochemically pure 59Fe was measured in man over one year with a 4 π-geometry whole-body radioactivity detector and utilized for the estimation of the effective half-life of 59Fe. The correct physical half-life of radiochemically pure 59Fe was used for the calculation of the biological half-life. Normal male subjects showed an effective half-life of 43.6 ± 0.34 days and a biological half-life of 2136 ± 807 days. This means a whole-body-59Fe-turnover rate of 0.032 ± 0.012%/d equivalent to 1.25 ± 0.46 mg Fe/d (for a whole-body iron pool of 3850 mg in a 70 kg man). Menstruating females were observed to have effective half-lives of 43.1 ± 0.22 days and therefore biological half-lives of 1389 ± 224 days. Their whole-body-59Fe-turnover rate is higher (than in males) with 0.050 ± 0.008%/d. For an optimal whole-body iron pool of 3300 mg (in 60 kg female) this would mean an iron loss of 1.65 ± 0.26 mg/d. Non-menstruating females were quite similar to males. They showed effective and biological 59Fe-half-lives of 43.5 ± 0.48 and 1833 ± 857 days, respectively. Their whole-body-59Fe-turnover rate was calculated to be 0.038 ± 0.018%/d or 1.25 ± 0.59 mg Fe/d (60 kg female with 3300 mg Fe-pool). These experimental data are the first direct and reliable proof for the magnitude of daily iron loss and iron requirements in man.

Molecular aspects of the regulation of rat kidney alkaline phosphatase

The mechanisms by which phosphate regulates the activity of alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) in rat kidney were investigated. Measurements of incorporation of [(14)C]leucine into kidney alkaline phosphatase in rats fed on complete or phosphate-free diet provide evidence of a twofold increase in the rate of synthesis of the enzyme in diet-treated animals. Cycloheximide experiments indicated that control and diet-adapted enzyme decreases in activity according to first-order kinetics with a calculated half-life of 10.3 and 6.5h after complete and phosphate-free diet administration respectively. Basal and diet-adapted enzymes exhibit similar K(m) values for several phosphomonoesters and an identical degree of inhibition is produced by cysteine. In addition, the enzyme from both sources is the same with regard to heat inactivation at 45, 56 or 64 degrees C, to the profile of elution from Sephadex and to electrophoretic properties on polyacrylamide gel. A failure of rat kidney alkaline phosphatase to respond to cortisol (hydrocortisone) was also observed.

Spontaneous reactivation of phosphorylated and carbamylated cholinesterases

This paper presents, in tabular form, extensive data on the rates of spontaneous reactivation of phosphorylated and carbamylated cholinesterases from numerous animal species. The half-lives clearly indicate the influence of the acyl group of the inhibitor and that of the source of the enzyme.

Effects of synergists on the metabolism and toxicity of anticholinesterases

Insecticide synergists enhance insecticidal action through their ability to block the enzymatic detoxification of insecticides with which they are combined. The structure of the synergist is therefore determined by the nature of the insecticide and the critical biochemical pathway responsible for its degradation.Synergists can be broadly classified as either analogue synergists, whose structure closely resembles that of the insecticide they synergize, or inhibitors of microsomal oxidation. Metabolism of the phenyl methylcarbamates is effected largely by the microsomal enzymes. Consequently microsomal enzyme inhibitors, such as the methylenedioxyphenyl compounds, the aryloxyalkylamines, the thiocyanates, the propynyl aryl ethers, and the 1,2,3-benzothiadiazoles, are all effective carbamate synergists. The detoxification pathways of the organophosphates, however, are more complex and include hydrolysis, dealkylation, and carboxylesterase pathways as well as oxidation. Because phosphorothioates are activated by oxidation, their toxicity is often antagonized by oxidase inhibitors. The effectiveness of different synergists towards resistant strains of insects is likely to vary in a manner that reflects the critical metabolic pathway on which resistance depends.