QUANTITATIVE SEPARATION OF RADIOACTIVE STEROLS AND BILE ACIDS IN HUMAN FAECES

A method is described for the quantitative separation of radioactive bile acids and neutral sterols in human faeces on a potassium hydroxide-treated silicic acid column. Results obtained with faecal extracts containing metabolites derived from radioactive cholesterol, cholic acid, and chenodeoxycholic acid show that the efficiency of extraction is at least 96% and that mutual contamination between the bile-acid and sterol fractions is between 0.7 and 3.8%. The method gives better results than one based on separation of the faecal steroids into saponifiable and unsaponifiable material.

PEPTIDE SYNTHESIS FROM AMINO ACIDS IN AQUEOUS SOLUTION

Four dipeptides and a tripeptide were formed when an aqueous solution of glycine and leucine was exposed to ultraviolet light in the presence of cyanamide.

OESTRADIOL METABOLISM IN THE PREVIABLE HUMAN FOETUS AND IN THE FOETO-PLACENTAL UNIT

Five normal previable foetuses were perfused with tracer amounts of oestradiol-4-14C and the metabolism of the compound was investigated. This study was completed by 3 experiments in which the oestradiol-4-14C was introduced in situ into the intact foeto-placental unit via the umbilical circulation.

More than 80 per cent of the radioactive material present in the various foetal organs in both types of experiments was in a conjugated form. In contrast, in the placentas, less than 10 per cent of the total radioactivity present was in a conjugated form.

The bulk of the radioactive material present in the foetal tissues was identified as oestradiol 3-sulphate and oestrone sulphate. In addition, two minor fractions were detected in the perfused foetuses, one of which behaved in countercurrent distribution studies as »glucosiduronates«; the other resembled »sulphates«. The oestrogen moiety of these two fractions was neither oestradiol nor oestrone, but it appeared to be a complex mixture. Although some radioactive material was found which closely resembled oestriol, it was not possible to detect oestriol with certainty.

No glucosiduronate-like material was found in the foetal tissues following the injection of oestradiol-4-14C into the intact foeto-placental unit. Also the quantity of the »sulphate-like« material different from oestradioland oestrone sulphates was greatly reduced:

A number of unconjugated metabolites were also detected, among which oestrone was identified.

A perfusion experiment with an anencephalic foetus indicated that this foetus was capable of forming conjugated metabolites from oestradiol-4-14C.

The results obtained do not favour the view that oestriol is a major and instantaneously formed foetal metabolite of oestradiol. On the other hand, they lend additional support to the concept that oestrogens reaching the foetus are extensively sulphurylated by the foetus and that these oestrogen sulphates are hydrolysed by the placenta before transfer of the oestrogen moiety to the maternal circulation.

REGULATION OF GLUCOSE OXIDATION IN THE WHITE RAT

The rate of oxidation of glucose has been measured in 43 rats acclimated to 30 C, at rates of turnover of 8–105 mg glucose carbon/100 g body wt. per hour (mg C/100 g·hr) by the technique of priming and continuous infusion of trace amounts of C14-glucose. This range of glucose turnover values had been obtained by using rats in various nutritive states or by continuous infusion of nonlabeled glucose. Oxidation was directly proportional to turnover between rates of turnover of 8 and 40 mg C/100 g·hr with a slope of about 0.5. At higher rates of turnover the ratio of oxidation to turnover decreased to 0.35, thus indicating that oxidation was approaching a maximum. At the highest rates of glucose turnover, a maximum of 63% of the respiratory CO2 was derived from body glucose, although the amount of non-labeled glucose carbon injected per minute exceeded the respiratory CO2 carbon by a factor of 1.8. Therefore, oxidation of glucose in the intact rat is closely regulated by its availability, but body glucose does not appear to serve as sole substrate for respiration even when its rate of turnover exceeds the respiratory output of carbon.

PATTERNS OF OXIDATIVE ASSIMILATION IN STRAINS OF PSEUDOMONAS AND ACHROMOBACTER

Tomlinson, Geraldine A. (University of British Columbia, Vancouver, B.C., Canada) and J. J. R. Campbell. Patterns of oxidative assimilation in strains of Pseudomonas and Achromobacter. J. Bacteriol. 86:434-444. 1963.-Oxidative assimilation of glucose-U-C(14) in the absence of added nitrogen was studied by use of washed-cell suspensions of Pseudomonas aeruginosa, P. fluorescens, Achromobacter strain B81, and Achromobacter viscosus (Alcaligenes viscolactis). The suggestion that oxidative assimilation in these organisms is the reincorporation of endogenously produced ammonia by way of alpha-ketoglutarate is tenable. Each of the four organisms accumulated intermediate compounds which acted as pacemakers for the oxidation of glucose. This phenomenon, partly because it ensured the availability of additional ammonia, undoubtedly increased the degree of oxidative assimilation. Products accumulating in the supernatant fluids during glucose oxidation were alpha-ketoglutarate, pyruvate, gluconate, a low molecular weight carbohydrate, and dicarboxylic acids. No two bacteria formed the same products. Assimilation of radioactivity into the cells, which accounted for 12 to 26% of the available C(14), continued as long as an oxidizable substrate was present, and was paralleled by uptake of endogenously produced ammonia. During the early stages of glucose oxidation, compounds of the cold trichloroacetic acid-soluble pool constituted a major portion of the total radioactivity of the cells. The lipid fractions of P. aeruginosa and Achromobacter B81 were also of high relative activity during this time. The labeling of the nucleic acid fractions of all four bacteria increased with time, more radioactivity being found in fractions from the two Achromobacter species than in those from the pseudomonads. At the completion of the experiment, the largest percentage of incorporated radioactivity was present in the protein fractions. One of the organisms, Achromobacter B81, synthesized a high molecular weight carbohydrate material.