The fate of 7[14C]-methylguanine after administration to the rat

1. To assess the significance of the methylation of nucleic acids known to be caused by certain carcinogens, the metabolic fate of 7[¹⁴C]-methylguanine was studied, with special reference to its possible incorporation into RNA and DNA. 2. The major part (approx. 95%) of the dose was excreted unchanged in the urine. A small amount of N-demethylation took place, as evidenced by the formation of radioactive adenine and guanine, and expiration of ¹⁴C-labelled carbon dioxide. No evidence was obtained for the direct incorporation of 7-methylguanine into systems synthesizing nucleic acids, i.e. RNA in liver, DNA in intestine or in the foetus.     

Binding of phosphatidylcholine-14C to glass

Lecithin-(14)C was found to bind to Pyrex glass. The percentage bound varied with different organic solvents, being greatest in dioxane solution. Thorough treatment of the glass with dimethyldichlorosilane prevents the binding, which suggests that charge-charge interactions are involved.     

The chemical synthesis and biological oxidation of 7α-hydroxy[26-14C]cholesterol, 7-dehydro[26-14C]cholesterol and 26-hydroxy[26-14C]cholesterol

1. 26-Hydroxycholesterol was obtained by reducing the methyl ester of (±)-3β-hydroxycholest-5-en-26-oic acid, which was synthesized from 25-oxonorcholesterol. 2. Methods for preparing 7α-hydroxycholesterol and 7-dehydrocholesterol were modified to allow the micro-scale preparation of these [¹⁴C]sterols from [26-¹⁴C]-cholesterol. 3. 26-Hydroxycholesterol was oxidized more readily than 7α-hydroxycholesterol, 7-dehydrocholesterol or cholesterol by mitochondrial preparations from livers of mice, rats, guinea pigs, common toads (Bufo vulgaris) and Caiman crocodylus. 4. (±)-3β-Hydroxy[26-¹⁴C]cholest-5-en-26-oic acid was oxidized very rapidly to ¹⁴CO₂ by mouse and guinea-pig mitochondria without evident discrimination between the two optical isomers. 5. An enzyme system that oxidizes 26-hydroxycholesterol to 3β-hydroxycholest-5-en-26-oic acid was identified in the soluble extract of rat-liver mitochondria. This enzyme could use NADP in place of NAD but was not identical with liver alcohol dehydrogenase (EC 1.1.1.1). 6. [26-¹⁴C]Cholesteryl 3β-sulphate was not oxidized by fortified mouse-liver preparations that oxidized [26-¹⁴C]cholesterol to ¹⁴CO₂.     

Stearoyl[1-14C]sulfogalactosylsphingosine ([14C]sulfatide) as substrate for cerebroside sulfatase assay

A convenient method for large scale preparation of stearoyl[1-¹⁴C]sulfogalactosylsphingosine has been developed. The first step consists in preparing the lysosulfatide intermediate with a good yield, which we have successfully performed. In the second step, the lysoderivative is coupled to [1-¹⁴C]stearic acid through the acyl chloride procedure. The labeled substrate thus synthetized appears to be particularly convenient for cerebroside sulfatase determination, because of the stability of the ¹⁴C isotope, compared to the other isotopes (tritium or ³⁵S) which have been previously used for the same purpose.     

14C uptake by Schistosoma mansoni from Biomphalaria glabrata exposed to 14C-glucose

Exposure of Biomphalaria glabrata infected with Schistosoma mansoni to ¹⁴C-glucose results in a greater uptake of original total snail label by the parasitized digestive gland-gonad, site of the developing daughter sporocysts and cercariae, than by the digestive gland-gonad of control animals. As a consequence of this greater uptake by the infected digestive gland-gonad, the albumen gland and remainder of the carcass of parasitized snails receive less label than do those areas in normal snails. Emergence of cercariae from the snail and daughter sporocyst mass account for a diversion of 12.6% of original total label from the infected snail itself. This diversion of label from the snail to the parasite may explain carbohydrate depletion in parasitized snails.     

Study of the distribution of C14-variamycin and C14-mitramycim after intravenous administration to mice]

Distribution of antitumor antibiotics, i.e. C14-variamycin and C14-mitramycin in the organs of albino mice after their intravenous administration in single doses was studied. Similarity in the distribution dynamics of both the antibiotics with respect to the animal organs was found. However, the level of variamycin as compared to that of mitramycin was much higher in the liver and especially the spleen. In the experiments with variamycin the radioactivity of the kidney tissue decreased more rapidly than in the experiments with mitramycin. Chromatographic analysis of the urine of the mice treated with C14-variamycin was performed. The labeled Variamycin was detected in the animal urine within 48 hours from the moment of the antibiotic administration. Its portion in the total amount of the radioactive products in the urine was 30 to 40% at various stages of the study.     

Sugar utilization by citrus juice cells as determined by [14C]-sucrose and [14C]-fructose feeding analyses

Sugar utilization by mature citrus juice cells was investigated in light of previous reports suggesting the inability of these cells to phosphorylate hexoses. Grapefruit juice sac cells were incubated in solutions of [¹⁴C]-sucrose or [¹⁴C]-fructose for 16 h during which ¹⁴CO₂ evolution was measured by trapping into soluene. After the incubation period, tissue was extracted in 5 % trichloroacetic acid or 80 % ethanol and extracts separated and identified by thin layer chromatography. Fructose was taken up and metabolized more rapidly than sucrose. In both cases, significant amounts of ¹⁴CO₂, [¹⁴C]-pyruvic and [¹⁴C]-citric acid were recovered after incubation. In separate experiments, hexokinase activity in tissue extracts was found to co-sediment with mitochondrial fractions but was not detected in the soluble fractions as previously reported. The data indicated that, contrary to earlier observations, mature citrus fruit juice cells contain the enzymatic machinery to metabolize soluble sugars. This is consistent with the glycolytic utilization of sugars in cells undergoing anaerobic respiration.     

Preparation of L-tyrosine-ring- 14 C, L-DOPA-ring- 14 C and related metabolites

The reversibility of the tyrosine phenol-lyase reaction has been utilized to develop a simple system in which phenol-¹⁴C is incorporated into l-tyrosine in high yield. By use of mushroom tyrosinase, catechol-¹⁴C can be prepared from phenol-¹⁴C and l-DOPA-¹⁴C from l-tyrosine-¹⁴C. Catechol-¹⁴C can also be incorporated into l-DOPA-¹⁴C by use of tyrosine phenol-lyase, giving the possibility of preparing DOPA with two labeling patterns in the ring when starting with phenol-¹⁴C. Two further tyrosine metabolites, para-coumaric acid and homogentisic acid, have also been enzymatically prepared with ¹⁴C in the ring.