Nutritional and hormonal control of lung and liver fatty acid synthesis.

During starvation and in streptozotocin-induced diabetes, the total activities of rat lung acetyl CoA carboxylase and fatty acid synthetase are reduced to one-third of the normal values. Refeeding of the starved animals or administration of insulin to diabetic animals restores the levels to the original values. The insulin effect is dose and time dependent. These data contrast with those in the liver, where a 30- to 50-fold depression of these enzymes is observed in the diabetic state and administration of insulin is actually followed by doubling of the activity over normal controls. Fat-free high-fructose diet (containing 60% fructose by weight) enhances the activities of liver enzymes 3- to 6-fold over the values of controls on laboratory diet but has no effect on the lung enzymes. Long-term feeding of fructose diet also increases the activities of liver enzymes from diabetic animals to twice the value of normal controls on laboratory diet. Insulin administration to fructose-fed diabetic animals restores the enzyme activities to those obtained with fructose-fed normal controls. However, the stimulation of lung enzymes of diabetic animals can be effected either by fructose or by insulin. Antigen-antibody titrations and measurements of the rate of protein synthesis show that the increased activity of the lung and liver fatty acid synthetase is due to enhanced content rather than increased specific activity. These data suggest that insulin or fructose effects on fatty acid-synthesizing enzymes are mediated through intermediate(s) whose concentration is affected in the experimental diabetes. Furthermore, all tissues may not have stringent insulin requirements since the lung enzymes can be stimulated by fructose alone.     

Control of the sequential utilization of glucose and fructose by Escherichia coli.

In Escherichia coli (ATCCI5224; ML308), glucose and fructose phosphotransferase systems (PT-systems) are constitutive but activities are increased five and 10-fold respectively by aerobic growth on their respective substrates in defined media. In mixtures, glucose is used preferentially and the fructose PT-system activity is kept at its minimum; but, on glucose exhaustion, it overshoots its steady-state level and growth continues on fructose without lag. Cyclic AMP prevents overshoot. Continuous cultures operating as turbidostats on mixtures of glucose and fructose do not use fructose if sufficient glucose is present to support growth. If less glucose is available, it is all used and sufficient fructose is metabolized concurrently to maintain the growth rate characteristic of glucose. Both PT-systems are inhibited by hexose phosphates. Presence of homologous substrate specifically sensitizes each PT-system to inactivation by N-ethylmaleimide (NEM). Glucose diminishes the ability of fructose to sensitize its PT-system to NEM. This effect parallels the inhibition of fructose utilization by glucose and suggests that glucose denies fructose access to the fructose-specific part of the PT-system.     

Radiorespirometric study of the utilization of exogenous sucrose,glucose and fructose by germinating apple pollen

Po?adí intensity, s jakou prodýchávají pylové lá?ky testované cukry z 0,3 M roztok?, je sacharosa> glukosa> invertní cukr> fruktosa. Stejné po?adí je zaehováno na cukr-agarových mediích s výjimkou prvých dvou hodin inkubace, během kterých jsou sacharosa, glukosa a fruktosa prodýchávány témě? stejnou rychlostí. Během této doby se v prost?edí fruktosy, stejně jako v kontrole bez cukru, nevytvo?ily pylové lá?ky, zatím za p?itomnosti sacharosy dosahovaly délky a? 450 µ. Jestli?e byla pou?ita pro radioaktivní cukry jako nosi? sacharosa, byla fruktosa-¹⁴C prodýchávána a? 12krát, glukosa-¹⁴C a? 6krât intensivnëji neá sacharosa-¹⁴C. Za pou?ití nosi?e sacharosa+glukosa ?i sacharosa+fruktosa (molárni poměry 1:1), prodýchávaji pylové lácky sacharosu-¹⁴C pomaleji ne? p?íslu?ny monosaeharid a rovně? pomaleji ne? z prost?edí samotnéé sacharosy. Jestli?e byla nosi?em sacharosy-¹⁴C glukosa nebo fruktosa, byla (v některých ?asových úsecíeh pokusu) produkce¹⁴CO₂ pylovými láckami několik desítek procent mohutněj?í ne? za pou?ití nosi?e sacharosového. Z prost?edí invertního cukru je p?ednostně prodýchäväna fruktosa. Je tedy kapacita pylových enzymových systém? za?leňujících sledované cukry do jejich dýchacích cest pro fruktosu>glukosu> sacharosu, co? je opa?né po?adí ne? platí pro intensitu r?stového ú?inku těchto cukr? a ne? jaké bylo zji?těno pro rychlost jejich prodýchávání, jestli?e nebyly navzájem kombinovány. Ve specifickém r?stovém efektu sacharosy nem??e tedy být primárním faktorem ani rychlost její absorpce, ani intensita jejího prodýcháváni. Rychlá utilisace samotné sacharosy je následkem intensivněj?ího r?stu v jejím prost?edí. Získané výsledky dále ukazují, ?e sacharosa je vyu?ívána p?edev?ím cestou její inverse, p?i ?em? je p?ednostně prodýchávána fruktosová slo?ka.     

Routes for fructose utilization by Escherichia coli

There are three main routes for the utilization of fructose by Escherichia coli. One (Route A) predominates in the growth of wild-type strains. It involves the functioning of the phosphoenolpyruvate:glycose phosphotransferase system (PTS) and a fructose operon, mapping at min. 48.7, containing genes for a membrane-spanning protein (fruA), a 1-phosphofructose kinase (fruK) and a diphosphoryl transfer protein (fruB), under negative regulation by a fruR gene mapping at min. 1.9. A second route (Route B) also involves the PTS and membrane-spanning proteins that recognize a variety of sugars possessing the 3,4,5-D-arabino-hexoseconfiguration but with primary specificity for mannose(manXYZ), mannitol (mtlA) and glucitol (gutA) and which, if over-produced, can transport also fructose. A third route (Route C), functioning in mutants devoid of Routes A and B, does not involve the PTS: fructose diffuses into the cell via an isoform (PtsG-F) of the major glucose permease of the PTS and is then phosphorylated by ATP and a manno(fructo)kinase (Mak+) specified by a normally cryptic 1032 bp ORF (yajF) of hitherto unknown function (Mak-o), mapping at min. 8.8 and corresponding to a peptide of 344 amino acids. Conversion of the Mak-o to the Mak+ phenotypeinvolves an A24D mutation in a putative regulatory region.     

Separation of fructose and glucose mixture by zeolite Y

Na-, K-, Ba-, and Ca-Y were employed for the separation of fructose and glucose in an adsorption column. Effects of temperature, solvent flow rate, amount of mixture injection, and exchangeable cations on the separation were investigated. Efficiency of separation was used as a criterion to characterize the effectiveness of the separation. The transport and kinetic parameters for the column separation were also presented. From simple pulse experiments and moment analysis, the obtained process information of equilibrium and dynamic parameters might be used to design, operate, and control the separation column. (c) 1992 John Wiley & Sons, Inc.     

Substrate utilization during exercise with glucose and glucose plus fructose ingestion in boys ages 10--14 yr.

We measured substrate utilization during exercise performed with water (W), exogenous glucose (G), and exogenous fructose plus glucose (FG) ingestion in boys age 10-14 yr. Subjects (n = 12) cycled for 90 min at 55% maximal O(2) uptake while ingesting either W (25 ml/kg), 6% G (1.5 g/kg), or 3% F plus 3% G (1.5 g/kg). Fat oxidation increased during exercise in all trials but was higher in the W (0.28 +/- 0.023 g/min) than in the G (0.24 +/- 0.023 g/min) and FG (0.25 +/- 0.029 g/min) trials (P = 0.04). Conversely, total carbohydrate (CHO) oxidation decreased in all trials and was lower in the W (0.63 +/- 0.05 g/min) than in the G (0.78 +/- 0.051 g/min) and FG (0.74 +/- 0.056 g/min) trials (P = 0.009). Exogenous CHO oxidation, as determined by expired (13)CO(2), reached a maximum of 0.36 +/- 0.032 and 0.31 +/- 0.030 g/min at 90 min in G and FG, respectively (P = 0.04). Plasma insulin levels decrease during exercise in all trials but were twofold higher in G than in W and FG (P < 0.001). Plasma glucose levels decreased transiently after the onset of exercise in all trials and then returned to preexercise values in the W and FG (approximately 4.5 mmol/l) trials but were elevated by approximately 1.0 mmol/l in the G trial (P < 0.001). Plasma lactate concentrations decreased after the onset of exercise in all trials but were lower by approximately 0.5 mmol/l in W than in G and FG (P = 0.02). Thus, in boys exercising at a moderate intensity, the oxidation rate of G plus F is slightly less than G alone, but both spare endogenous CHO and fat to a similar extent. In addition, compared with flavored W, the ingestion of G alone and of G plus F delays exhaustion at 90% peak power by approximately 25 and 40%, respectively, after 90 min of moderate-intensity exercise.     

Generalized linearization of kinetics of glucose isomerization to fructose by immobilized glucose isomerase

The kinetic parameters of both glucose isomerization to fructose and immobilized glucose isomerase (GI) inactivation calculated under different conditions are compared and discussed. Utilizing these figures, the possibility of generalizing a linear model, previously proposed for the kinetics of glucose isomerization by immobilized glucose isomerase, is investigated, so as to apply them to whole ranges of temperature and concentrations of actual interest in industrial processes. The proposed model is a satisfactory approximation of the more involved Briggs-Haldane approach and substantially simplifies the problem of optimizing an industrial fixed-bed column for high-fructose corn syrup (HFCS) production.     

Prediction of the rate of glucose utilization from cellular levels of glucose 6-phosphate and fructose 1,6-diphosphate in Escherichia coli.

A comprehensive equation, upsilon = VM/[1 + (A0.5/Fru-P2)n] [ 1 + (Glc-6-P/I0.5)], has been proposed to represent the quantitative interrelationships between the rate of glucose utilization and the levels of glucose-6-phosphate and fructose-1,6-diphosphate in the intact Escherichia coli cell. This comprehensive equation was derived from empirical equations that describe the relationship between the rate of glucose utilization and one of these hexose phosphates in metabolic situations where the other hexoses phosphate was not altered. In the experiments described in this report, treatment of nitrogen (NH4+)-starved cultures of E. coli W4597 (K) with various concentrations of sodium azide altered the levels of both hexose phosphates as well as the rate of glucose utilization. In each case the observed rate and the rate predicted by the comprehensive equation agreed closely, substantiating the validity of this comprehensive relationship as a quantitative indicator of metabolic events in the intact cell. The mechanism of metabolic regulation that is represented by this equation is discussed in light of the cellular levels of adenosine 5'-triphosphate and phosphoenolpyruvate observed in these experiments.