Absence of rapid exchange component in a low-affinity carrier transport

A previous study showed that human red blood cells equilibrate much less rapidly with D-glucose at moderately high concentrations than with C(14)-glucose added after the net movement is completed. This had been predicted from a simple reversible mobile-carrier mediated-transport model system suggested by the net monosaccharide transport kinetics in these cells, but is also consistent with the more complex models proposed for certain active transport systems to account for elevation of tracer fluxes of even low-affinity "substrates" when their trans-concentration is raised. The simple model predicts, however, that with any sugar showing a much lower apparent affinity for the reactive sites, such as D-ribose, this phenomenon would not be observed, and tracer equilibration should proceed at approximately the same rate as net uptake. The latter expectation was confirmed experimentally by analyses of the ribose, or radioactivity, content of washed red cells sampled serially during incubation with ribose or C(14)-ribose in the appropriate mixtures. The tracer ribose movement showed no evidence of a relatively rapid exchange component. The relative rapidity of glucose tracer uptake into cells preloaded with ordinary glucose may therefore more readily be attributed simply to depression of tracer efflux by competition for the saturated reactive sites, than to any action of the trans-concentration on the influx by way of a coupled exchange process.

INFLUENCE OF DEOXYRIBONUCLEIC ACID DEGRADATION PRODUCTS AND ORTHOPHOSPHATE ON DEOXYNUCLEOTIDE KINASE ACTIVITY AND DEOXYRIBONUCLEIC ACID SYNTHESIS IN PNEUMOCOCCUS TYPE 3

Firshein, William (Wesleyan University, Middletown, Conn.). Influence of deoxyribonucleic acid degradation products and orthophosphate on deoxynucleotide kinase activity and deoxyribonucleic acid synthesis in pneumococcus type III. J. Bacteriol. 90:327-336. 1965.-An oligodeoxynucleotide fraction derived from a deoxyribonuclease-treated calf-thymus deoxyribonucleic acid (DNA) can enhance the activity of deoxycytidylic acid (dCMP) and deoxyguanylic acid (dGMP) kinases in cell suspensions of type III pneumococci. High levels of orthophosphate can produce similar effects. For part of the incubation period, the activity of dCMP and dGMP kinases is very low or undetectable in unsupplemented-cell suspensions of pneumococci. In contrast, the remaining kinases, deoxyadenylic acid and thymidylic acid, which are present in ample amounts in control and supplemented cells throughout the incubation period, are unaffected by the addition of oligodeoxynucleotides and orthophosphate. The stimulation of kinase activity is amino acid-dependent and can be abolished by adding chloramphenicol. When the oligodeoxynucleotide fraction and orthophosphate are further supplemented with all eight of the naturally occurring deoxynucleosides and deoxynucleotides (which do not affect kinase activity), a preferential enhancement of DNA synthesis occurs in comparison with cell growth or protein synthesis. Addition of deoxynucleosides and deoxynucleotides to unsupplemented cells produces only a slight increase in DNA synthesis. The preferential enhancement of DNA synthesis can be prevented by adding chloramphenicol at a certain time during incubation.

EFFECT OF AMINO ACIDS ON STEADY-STATE GROWTH OF A GROUP A HEMOLYTIC STREPTOCOCCUS

Davies, Helen C. (University of Pennsylvania, Philadelphia), Fred Karush, and Joanne H. Rudd. Effect of amino acids on steady-state growth of a group A hemolytic streptococcus. J. Bacteriol. 89:421-427. 1965.-A study has been made of amino acid utilization by a strain of type 4, group A streptococcus growing under steady-state conditions in a continuous-culture device and supplied with a completely synthetic medium. At a fixed growth rate, corresponding to a generation of time of 84 min, and with the pH maintained constant at 7.4, the bacterial turbidity was made dependent on the concentration of one of the amino acids of the defined medium. Under these conditions, the extracellular concentration of the limiting amino acid is fixed by the preset growth rate. The steady-state concentration of each of 14 essential l-amino acids was measured by means of C(14)-labeled amino acids in such limited cultures. At approximately equal turbidities, these concentrations ranged from 1.6 x 10(-6)m for methionine to 4.3 x 10(-4)m for glutamic acid. The rates of utilization of the amino acids ranged from 26 mmumoles per mg (dry weight) of bacteria per hr for histidine to 310 mmumoles per mg (dry weight) of bacteria per hr for glutamic acid. The percentage of the limiting amino acid used varied from 95% for threonine and methionine to 43% for gluamic acid. The rate of utilization of the limiting amino acid at unit concentration (tmoles per gram per hour per m) differed by a factor of 27 between extremes. These observations reflect the variation in the capacity of this streptococcal cell to take up and use different amino acids.

EFFECT OF INTESTINAL BYPASS ON CHOLESTEROL ABSORPTION AND BLOOD LEVELS IN THE RABBIT

A chronic in vivo preparation for the study of cholesterol absorption is described. Ten rabbits which had undergone ileocecal valvuloplasty, ten rabbits subsequent to upper small intestinal bypass and ileocecal valvuloplasty, and ten rabbits with lower small intestinal bypass (including the ileocecal valve), are compared to ten normal controls, on the basis of blood radioactivity, and whole blood cholesterol levels, following a force-fed standard test dose of cholesterol-4-C14, 10 mg, 0.4 µc/mg. The conclusions arrived at from the data are that the entire small intestine is capable of absorbing cholesterol, that bypass of either the upper or the lower half of the small intestine results in a marked (> 80%) reduction in the blood radioactivity subsequent to the oral test dose, and that there is a functional difference between the upper and the lower small intestinal bypass groups. Transit time in the small intestine appears to play a major role in the amount of cholesterol absorbed. To achieve both a marked lowering of cholesterol absorption and circulating cholesterol levels, the most efficacious surgical site of bypass of the small intestine is the ileum.

CO-2 FORMED FROM ENDOGENOUS AND EXOGENOUS SUBSTRATES IN PERFUSED RAT HEART

Measurements of total CO2 and C14O2 production by the isolated, perfused rat heart showed the extent of respiration dependent on endogenous and exogenous substrates. Glucose, acetate, and palmitate, but not glutamic acid or leucine, contributed appreciably to respiration. With optimal glucose and palmitate oxidation endogenous substrates accounted for over half of CO2. Endogenous substrates were adequate to maintain respiration for 30 but not for 60 min. Dependence of respiration on lipids was suggested by the similarity of metabolic CO2 in glycogen-depleted hearts perfused with no added substrate, with palmitate-1-C14, and with glucose-U-C14 plus palmitate. A reduction in C14O2 and in total CO2 formation with glucose-U-C14 in the presence of palmitate provided further support for the preferential oxidation of fatty acids. The Vo2, estimated from the total and C14O2, and an assumed respiratory quotient, indicated adequate oxygenation of the heart in the closed recirculated system. The necessity of maintaining an adequate coronary artery flow rate was indicated by an altered pattern of cell metabolism in hearts with reduced coronary perfusion.

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.

PHYSIOLOGICAL STATE OF ESCHERICHIA COLI AND THE INHIBITION OF DEOXYRIBONUCLEIC ACID SYNTHESIS BY PHENETHYL ALCOHOL

Treick, R. W. (Indiana University, Bloomington), and W. A. Konetzka. Physiological state of Escherichia coli and the inhibition of deoxyribonucleic acid synthesis by phenethyl alcohol. J. Bacteriol. 88:1580-1584. 1964.-The effects of concentration of phenethyl alcohol (PEA) and the physiological state of the cells on inhibition of macromolecular synthesis in Escherichia coli were investigated. Deoxyribonucleic acid (DNA) synthesis by cells of E. coli from the maximum stationary phase is completely inhibited by 0.32% (v/v) PEA immediately upon addition of the inhibitor, although there is a net increase in the synthesis of ribonucleic acid (RNA) and protein. However, DNA synthesis in cells from the exponential phase is inhibited only after an increase which corresponds to 1.4 to 1.6 times the amount of DNA present at the time of PEA addition. In a randomly dividing culture, this increment of DNA synthesis presumably represents completion of the DNA replication cycle initiated at the time of PEA addition. By programming the addition and removal of PEA, DNA synthesis can be made to proceed in stepwise increments corresponding to doublings of the DNA. The data indicate that the DNA being replicated at the time of PEA addition completes the replication cycle and, although there is net synthesis of RNA and protein, no initiation of a second cycle of DNA replication occurs until the removal of the inhibitor.

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.