Rate Of 14CO2 Evolution Research Articles

Towards a better understanding of carbon flow in the rhizosphere: a time-dependent approach using carbon-14

Controversies exist in interpreting rhizosphere C flow obtained by different 14CO2 labelling methods. However, there is a need for the standardisation of methods in order to be able to compare values obtained for different plants, different stages of development and different habitats. Perennial bromegrass (Bromus erectus Huds) grown in soils of different fertility was exposed to a 14CO2 atmosphere for different periods of time: 1 h, 298 h and 78 days. The evolution of 14CO2 in the soil was measured during and after labelling. The 14C contents of plant and rhizosphere compartments were then estimated. The time-sequence of the rate of 14CO2 evolution after 1 h of labelling, indicated a maximum after around 20 h, followed by an exponential decrease. When expressed as a percentage of net 14C assimilation, root-soil respiration accounted for 14% and 18% in the nutrient-poor and nutrient-rich soils, respectively. Integration of the hourly values over several days showed that the dynamics of the evolution rate were similar for the 298-h and 78-day experiments, thus indicating that rhizosphere C flow was dominated by newly assimilated C. This was confirmed by the proportions of below-ground 14C, measured for roots, respiration and soil, which were not significantly affected by the labelling regime. The differences were, however, found to be significant between the two types of soils. The conclusion was that the conditions for plant growth during labelling were more important than the length of time of labelling, and that this explained the discrepancies in the literature-cited values. A succession of short-term 14C labelling of plants at different development stages followed by an allocation period of about 1 week is proposed to give a reliable estimation of the dynamics of C flow in the rhizosphere.

Mineralization of Amino Acids Applied to Soils Impact of Soil Sieving, Storage, and Inorganic Nitrogen Additions

The effect of inorganic N additions on the biodegradation and microbial use of organic N pools in soil is poorly understood. To examine the effects of inorganic N on the mineralization rates of amino acids, four soils under contrasting management regimes were subjected to increasing loadings of NH4NO3, ranging from 0 to 120 kg N ha−1 In addition, the effect of soil sieving and storage temperature and time on amino acid mineralization was also investigated. At times ranging from 1 to 40 d after the addition of the inorganic N, the mineralization kinetics of an equimolar mixture of fifteen 14C‐labeled amino acids was followed for a subsequent 24‐h period. The rate of 14CO2 evolution was soil dependent, with half‐lives ranging from 2 h for topsoils to 25 h for subsoils. For all soils, at all times, and at all inorganic‐N loadings, the addition of inorganic N appeared to have little effect on the mineralization kinetics of the amino acids to 14CO2 In addition, the presence of inorganic N also had no major effect on the C use efficiency of the microbial biomass. It is speculated that N release from the amino acids into the soil by the microbial biomass may also be little affected by inorganic‐N additions. Sieving and storage of soil at either 4 or 18°C for up to 40 d had little impact on amino acid mineralization rate. Experiments with potential microbial disrupting agents (autoclaving, CHCl3 fumigation, HgCl2, and freeze–thaw) all indicated that the observed mineralization of amino acid C was due to microbial activity. We conclude therefore that inorganic N and soil storage has little effect on the microbial use of readily assimilatable amino acids.

Effect of carbon:nitrogen ratio on kinetics of phenol biodegradation by Acinetobacter johnsonii in saturated sand.

In polluted soil or ground water, inorganic nutrients such as nitrogen may be limiting, so that Monod kinetics for carbon limitation may not describe microbial growth and contaminant biodegradation rates. To test this hypothesis we measured 14CO2 evolved by a pure culture of Acinetobacter johnsonii degrading 120 micrograms 14C-phenol per ml in saturated sand with molar carbon:nitrogen (CN) ratios ranging from 1.5 to 560. We fit kinetics models to the data using non-linear least squares regression. Phenol disappearance and population growth were also measured at CN1.5 and CN560. After a 5- to 10-hour lag period, most of the 14CO2 evolution curves at all CN ratios displayed a sigmoidal shape, suggesting that the microbial populations grew. As CN ratio increased, the initial rate of 14CO2 evolution decreased. Cell growth and phenol consumption occurred at both CN1.5 and CN560, and showed the same trends as the 14CO2 data. A kinetics model assuming population growth limited by a single substrate best fit the 14CO2 evolution data for CN1.5. At intermediate to high CN ratios, the data were best fit by a model originally formulated to describe no-growth metabolism of one substrate coupled with microbial growth on a second substrate. We suggest that this dual-substrate model describes linear growth on phenol while nitrogen is available and first-order metabolism of phenol without growth after nitrogen is depleted.

Importance of Catalase in the Disposal of Hydrogen Peroxide Within Human Erythrocytes

The catalase within normal, intact human erythrocytes was completely inactivated with amino triazole. The rate of 14CO2 evolution, when the cells were subsequently incubated with 14C-labeled glucose, provided a measure of the rate at which NADPH was being oxidized by the glutathione peroxidase/reductase system for the disposal of H2O2. This rate was determined in control cells and in catalase-inactivated cells while the cells were exposed to H2O2, which was generated at various constant and predetermined rates by glucose oxidase. The results indicated that catalase handles approximately half of the generated H2O2. The glutathione peroxidase/reductase mechanism accounted for the other half. These results are in agreement with our earlier findings on erythrocytes of a subject with a genetic deficiency of catalase. However, an unexpected result with the present approach was the finding that the increased dependence on the glutathione peroxidase/reductase mechanism did not occur until greater than 98% of the catalase had been inactivated. The latter observation indicates that catalase and the glutathione peroxidase/reductase system function intracellularly in a manner very different from that previously ascribed to them. An explanation of the findings requires that the two methods of H2O2 disposal function in a coordinated way, such as a sequential action in which the glutathione peroxidase/reductase system is the rate-limiting step.

Importance of catalase in the disposal of hydrogen peroxide within human erythrocytes

The catalase within normal, intact human erythrocytes was completely inactivated with amino triazole. The rate of 14CO2 evolution, when the cells were subsequently incubated with 14C-labeled glucose, provided a measure of the rate at which NADPH was being oxidized by the glutathione peroxidase/reductase system for the disposal of H2O2. This rate was determined in control cells and in catalase-inactivated cells while the cells were exposed to H2O2, which was generated at various constant and predetermined rates by glucose oxidase. The results indicated that catalase handles approximately half of the generated H2O2. The glutathione peroxidase/reductase mechanism accounted for the other half. These results are in agreement with our earlier findings on erythrocytes of a subject with a genetic deficiency of catalase. However, an unexpected result with the present approach was the finding that the increased dependence on the glutathione peroxidase/reductase mechanism did not occur until greater than 98% of the catalase had been inactivated. The latter observation indicates that catalase and the glutathione peroxidase/reductase system function intracellularly in a manner very different from that previously ascribed to them. An explanation of the findings requires that the two methods of H2O2 disposal function in a coordinated way, such as a sequential action in which the glutathione peroxidase/reductase system is the rate-limiting step.

Double-blind evaluation of BACTEC and Buddemeyer-type radiorespirometric assays for in vitro screening of antileprosy agents.

Two radiorespirometric assays, the BACTEC 460 and Buddemeyer-type 14CO2 detection systems, were evaluated in a double-blind manner for their ability to discriminate between authentic antileprosy agents and inactive compounds. Freshly harvested, nude-mouse derived Mycobacterium leprae were incubated in axenic media in the presence of coded test solutions prepared in a remote laboratory. Activity was assessed by comparing the rate of 14CO2 evolution from [1-14C]palmitic acid to controls. Breaking the code revealed that both systems demonstrated a dose response to ethionamide, pefloxacin and rifampicin as well as sensitivity to dapsone. Most of the water, ethanol, sucrose, dabsyl chloride and riboflavin negative-control samples failed to effect a significant reduction in radiorespirometric activity. This study confirms the ability of the radiorespirometric assays to function as a primary drug screening system in leprosy.

Biodegradation process and the nature of metabolism of metalaxyl in soil

SUMMARYThe enhanced biodegradation of metalaxyl was studied in tobacco, citrus, avocado and corn soils. The most rapid degradation of metalaxyl occurred in a tobacco soil in which the half‐life (50% degradation) of metalaxyl was 6 days. The main breakdown product of metalaxyl in all soils was the acid metabolite. Ring labelled [14C]metalaxyl incubated for 4 wk in 6 soils demonstrated a low rate of 14CO2 evolution ranging from 2.1% to 11.3% which was unrelated to the biodegradation properties of the soil. A relationship between the concentration of metalaxyl and the subsequent rate of biodegradation was found in the tobacco soils. Higher concentrations of metalaxyl resulted in faster biodegradation rates. A single exposure of tobacco and corn soils to metalaxyl (100 μg/ml or 200 μg/g dry weight of soil) significantly increased their subsequent capacity to degrade the fungicide. Addition of the fungicide thiram or the antibiotics streptomycin and chloramphenicol to an avocado soil resulted in 75% and 51% inhibition of metalaxyl degradation, respectively. A combination of the fungicide and antibiotics resulted in 89% inhibition. The results indicate that enhanced microbial degradation of metalaxyl can occur in a wide range of soils. Under experimental conditions using soil solutions or soil systems, a single application of the fungicide may trigger this event. A wide range of fungi and bacteria appear to take part in degrading metalaxyl.

Oxidation of palmitic acid by Mycobacterium leprae in an axenic medium.

The ability of Mycobacterium leprae to oxidize palmitic acid during incubation in an axenic medium was studied. By using a Buddemeyer-type detection system, partially purified nude-mouse-derived M. leprae was found to produce 14CO2 from 14C-labeled palmitic acid in a linear fashion for at least 1 week. Procedures known to remove residual host tissue did not diminish the rate of 14CO2 evolution, indicating that bacterial metabolism was being measured. Palmitate oxidation was temperature sensitive, with an apparent optimum of 33 degrees C, but pH insensitive. Bacilli exposed to a variety of antileprosy drugs for 1 or 2 weeks displayed significantly reduced rates of 14CO2 evolution upon subsequent addition of 14C-labeled palmitic acid. This activity could be readily detected with 10(6) bacilli, thus indicating its potential for use in clinical susceptibility testing.

Tolerance of Birdsfoot Trefoil (Lotus corniculatus) to 2,4-D

Translocation and metabolism of14C-2,4-D [(2,4-dichlorophenoxy)acetic acid] and effects of 2,4-D on protein synthesis were compared in ‘T–68’ (2,4-D tolerant) and ‘Viking’ (susceptible) birdsfoot trefoil (Lotus corniculatusL.) in an attempt to elucidate some tolerance mechanisms. After14C-2,4-D was applied to upper trifoliate leaves, significantly less 2,4-D was found in stems, in leaves below the treated leaves, and in roots of T–68 compared to Viking. More 2,4-D was bound to alcohol-insoluble cellular constituents of T–68 leaves, stems, and roots. When alcohol-soluble components were fractionated, slightly more14C water-soluble compounds were found in T–68, indicating further inactivation by glycosylation. No amino acid-2,4-D conjugates were found. The rate of14CO2evolution from14C-2,4-D treated seedlings in T–68 was five times that in Viking. Protein synthesis appeared to be more rapid in T–68 but the relationship to 2,4-D was not clear. In part, 2,4-D resistance in T–68 may result from its ability to inactivate 2,4-D by differential binding and conjugation and by side chain breakdown as indicated by14CO2release.

The Influence of Temperature, Moisture, and Prior EPTC Application on the Degradation of EPTC in Soils

Laboratory and field studies were conducted to compare the degradation rate of EPTC (S-ethyl dipropylthiocarbamate) in soils with a previous history of EPTC application vs. soils with no prior EPTC application. Laboratory experiments showed a rapid breakdown of14C-carbonyl EPTC to14CO2in Kennebec silt loam (sil) and Tripp very fine sandy loam (vfsl) with prior exposure to EPTC. A single prior application of EPTC to Tripp vfsl was sufficient to increase the rate of14CO2evolution. The rate of EPTC degradation in Tripp vfsl with a history of EPTC exposure was dependent on soil moisture from below 3% and independent of moisture above 3%. Patterns of degradation at 5, 15, and 25 C in the Kennebec sil with and without prior history were described by exponential decay. EPTC was degraded more rapidly at 15 and 25 C in the Kennebec sil with a prior EPTC history. Under field conditions the breakdown of EPTC in a Kennebec sil with and without prior exposure to EPTC was similar to laboratory results.

Relationships between Pyruvate Decarboxylation and Branched-Chain Volatile Acid Synthesis in Ascaris Mitochondria

The rate of 14CO2 evolution from 1-[14C]pyruvate by intact Ascaris mitochondria was very slow, but increased with increasing concentrations of pyruvate. At all concentrations of pyruvate, in an aerobic environment, pyruvate decarboxylation was stimulated greatly by the addition of fumarate, malate, or succinate. However, under anaerobic conditions, only malate and fumarate stimulated pyruvate decarboxylation; succinate had no effect. This implies that the aerobic metabolism of succinate, presumably to other dicarboxylic acids, may be required for the stimulation. Incubation of sonicated mitochondria with pyruvate plus fumarate, under rate-limiting concentrations of NAD+, resulted in approximately equal quantities of pyruvate utilized and succinate formed, suggesting that pyruvate oxidation and fumarate reduction may be linked. Branched-chain, volatile fatty acids were not formed during incubations with either malate or succinate, or succinate plus acetate. However, incubations of intact Ascaris mitochondria with pyruvate plus succinate yielded 2-methylbutyrate and 2-methylvalerate, whereas incubations with pyruvate plus propionate yielded almost exclusively 2-methylvalerate. Oxygen dramatically inhibited the synthesis of the branched-chain acids from succinate plus pyruvate, attesting to the apparent anaerobic nature of Ascaris mitochondrial metabolism. Significantly, the addition of glucose plus ADP stimulated the formation of all volatile fatty acids. Therefore, the synthesis of branched-chain acids may be related directly to increased energy generation. Alternatively, they may function in the regulatory role of maintaining the mitochondrial redox balance.

Dual effect of carbonic anhydrase inhibitors on H+ transport by the turtle bladder.

Previous studies in isolated turtle bladder have demonstrated that high concentrations of carbonic anhydrase (CA) inhibitors limit H+ transport (JH) by reducing the catalyzed rate of CO2 hydroxylation and also by inhibiting some other step in the acidification process. One possibility is that these inhibitors alter the energy substrate requirement for JH. Recent work has demonstrated that JH may be dependent in part on glucose oxidation via the pentose shunt (PS). The present study was undertaken to determine whether CA inhibitors exert a direct effect on PS metabolism by turtle bladder. Acetazolamide and benzolamide at concentrations of 5 X 10(-4) M significantly reduced the rate of 14CO2 evolution from [1-14C]- but not [6-14C]glucose after JH was abolished by an adverse electrochemical gradient for JH+. These changes are consistent with a reduction in PS metabolism. These same sulfonamides also reduced glucose-6-phosphate dehydrogenase (G-6-PD) activity in mucosal cell homogenates. Acetazolamide decreased the Vmax of G-6-PD but not the Km and, therefore, appears to be a noncompetitive inhibitor of G-6-PD with an estimated Ki of 10(-4) M. The t-butyl analogue of acetazolamide, CL 13850, which is without CA inhibitory activity, had no measurable effect on G-6-PD activity. Accordingly, it is suggested the sulfonamide CA inhibitors may reduce JH by two modes of action, inhibition of CA and inhibition of G-6-PD.

Radiorespirometry of Candida utilis in phased culture under nitrogen-, carbon-, and phosphorus-limited growth.

The release of 14CO2 from specifically labelled glucose ([G-1-14C],[G-2-14C],[G-3,4-14C], and [G-6-14C]) by phased cells of C. utilis was examined at intervals during 6-h cycles under conditions of N-,P-, and C-limited growth. On the basis that the release of 14CO2 from [G-1-C14] could serve as a measure of hexose monophosphate pathway (HMP) activity, of 14CO2 from [G-3,4-14C] as a measure of Embden-Meyerhof-Parnas (EMP) activity, and 14CO2 from [G-6-14C] as indicative of tricarboxylic acid (TCA) cycle activity, it was concluded that a relatively uniform operation of EMP occurred throughout the cycle in N-, P-, and C-limited cells, and of HMP and TCA in C-limited cells, but considerable variations took place in HMP and TCA cycle activities in N- and P-limited cells. The patterns of 14CO2 released from [G-2-14C] were more closely related to those observed from [G-1-14C] and [G-3,4-14C] than from [G-6-14C]. Changes in the rate of 14CO2 evolution during the cycle were sometimes abrupt and likely coincided with 'critical points' of metabolic activity in the cycle.

The adsorption and degradation of glyphosate in five Hawaiian sugarcane soils*

Summary:The rate of aerobic evolution of 14CO2 from 14C‐glyphosate labelled in the methylphosphonyl carbon, varied 100‐fold within a group of five Hawaiian sugarcane soils. The rate depended inversely on the degree of soil binding, probably associated with the phosphonic acid moiety, and to a less certain extent on soil pH and soil organic matter. After an initial rapid degradation, the rate of 14CO2 evolution in three soils reached a constant at 16–21 days which continued to the 60‐day termination. The other two soils showed a continually decreasing rate throughout. Two soils released over 50% of the labelled carbon in 60 days, a third released 35%, while the remaining soils released 1.2 and 0.8% respectively.Labelled carbon in the soils after 60 days consisted of glyphosate and one metabolite, aminomethyl‐phosphonic acid, with glyphosate predominating in high fixing soils. The 14C could be extracted almost completely with NaOH solution, and remained mainly in solution after acidification.

An experimental study of cellulose and hemicellulose degradation in the alimentary canal of the American cockroach

Artificial diets containing [14C]cellulose and [14C]hemicellulose were prepared and fed to adult females. During the first 300 h after ingestion, 14CO2 was recovered equivalent to about 73% (cellulose) and 48% (hemicellulose) of the label ingested. For both polysaccharides the rate of 14CO2 evolution peaked 20–40 h after feeding and label was acquired by hemolymph trehalose. The evolution of 14CO2 from labelled cellulose was sharply reduced when antibiotics were supplied in the diet either with the labelled polysaccharide or before its ingestion. When each polysaccharide was introduced into the lumen of the cannulated colon in vitro, degradation occurred and acid- and heat-stable labelled material appeared in the incubation medium. It is proposed that cellulose and hemicellulose are potentially of nutritional significance in this insect and that the hindgut may be an important site of degradation.

Active H+ transport in the turtle urinary bladder. Coupling of transport to glucose oxidation.

The turtle urinary bladder acidifies the contents of its lumen by actively transporting protons. H+ secretion by the isolated bladder was measured simultaneously with the rate of 14CO2 evolution from [14C]glucose. The application of an adverse pH gradient resulted in a decline in the rate of H+ secretion (JH) and in the rate of glucose oxidation (JCO2). The changes in JH and JCO2 were linear functions of the pH difference across the membrane. Hence, JH and JCO2 were linearly related to each other. The slope, deltaJH/deltaJCO2 was found to be similar in half-bladders from the same animal but was seen to vary widely in a population of turtles. To investigate the effect of pH gradients on deltaJH/deltaJCO2, two experiments were performed in each of 14 hemibladders. In one, JH and JCO2 were altered by changing the luminal pH. In the other, they were altered by changing the ambient pCO2 while the luminal pH was kept constant. The average slope, deltaJH/deltaJCO2, in the presence of pH gradients was 14.45 eq-mol-1. In the absence of gradients in the same hemibladders it was 14.72, delta = 0.27 +/- 1.46. The results show that H+ transport is organized in such a way that leaks to protons in parallel to the pump are negligible. Analysis of the transport system by use of the Essig-Caplan linear irreversible thermodynamic formalism shows that the system is tightly coupled. The degree of coupling, q, given by that analysis was measured and found to be at or very near the maximum theoretical value.

Role of arginine deiminase in growth of Mycoplasma hominis.

Arginine has been considered as the major energy source of nonglycolytic arginine-utilizing mycoplasmata. When three strains of Mycoplasma arginini, and one strain each of Mycoplasma arthritidis, Mycoplasma fermentans, Mycoplasma gallinarum, Mycoplasma gallisepticum and Mycoplasma hominis were grown in the medium with high arginine concentration (34 mM) compared with low arginine (4 mM), both the protein content of the organisms and the specific activity of arginine deiminase increased. M. fermentans, the one arginine-utilizing species included in the survey which is also glycolytic, showed an increase in protein content but no increase in specific activity of the enzyme. The glycolytic non-arginine-utilizing M. gallisepticum did not show an increase in either parameter. The Km for arginine deiminase from crude cell extracts was 1.66 X 10(-4)M. The enzyme demonstrated a hyperbolic activation curve subject to substrate inhibition and was not affected by the presence of L-histidine. When mycoplasmic protein and arginine deiminase were determined for M. hominis under aerobic and anaerobic conditions, aerobically grown cells exhibited no detectable enzymatic increases until late in log phase. Higher levels of arginine deiminase were observed earlier in the anaerobic growth cycle. The rate of 14CO2 evolution from [guanido-14C]arginine was not altered in arginine-supplemented cells compared with cells grown in low arginine. In addition, CO2 production did not parallel increased arginine deiminase activity. These observations argue that arginine is used only as an alternate energy source in these organisms.

Indoleacetic Acid Metabolism in Cuttings of Plum (Prunus cerasifera × P. munsoniana cv. Marianna 2624)1

Abstract Treatment of ‘Marianna 2624’ plum cuttings for 7 days with 1-14C-IAA with or without a pretreatment with 4000 ppm indolebutyric acid (IBA) for 5 sec revealed that the synthetic hormone inhibited IAA oxidase activity as measured by the decreased rate of 14CO2 evolution. KOH hydrolysis of different radioactive zones on paper chromatograms derived from alcoholic extractives of cuttings yielded presumptive IAA upon re-chromatography. Likewise, KOH and peptidase treatment of the alcohol insoluble residue yielded a radioactive substance with chromatographic properties characteristic of IAA. The presence of presumptive IAA and ninhydrin-positive substances in the peptidase hydrolyzate indicate that IAA was bound to protein(s). Appreciable radioactivity still remained in the alcohol insoluble residue after protein hydrolysis.

Acetoacetate metabolism in infant and adult rat brain in vitro.

1. Acetoacetate or dl-beta-hydroxybutyrate increases the rate of oxygen consumption to a smaller extent than that brought about by glucose or pyruvate in adult rat brain-cortex slices but to the same extent as that in infant rat brain-cortex slices. 2. The rate of (14)CO(2) evolution from [1-(14)C]glucose considerably exceeds that from [6-(14)C]glucose in respiring infant rat brain-cortex slices, in contrast with adult brain-cortex slices, suggesting that the hexose monophosphate shunt operates at a greater rate in the infant rat brain than in the adult rat brain. 3. The rate of (14)CO(2) evolution from [3-(14)C]acetoacetate or dl-beta-hydroxy[3-(14)C]butyrate, in the absence of glucose, is the same in infant rat brain slices as in adult rat brain slices. It exceeds that from [2-(14)C]glucose in infant rat brain but is less than that from [2-(14)C]glucose in adult rat brain. 4. Acetoacetate is oxidized in the brain through the operation of the citric acid cycle, as shown by the accelerating effect of glucose on acetoacetate oxidation in adult brain slices, by the inhibitory effects of malonate in both infant and adult brain slices and by its conversion into glutamate and related amino acids in both tissues. 5. Acetoacetate does not affect glucose utilization in adult or infant brain slices. It inhibits the rate of (14)CO(2) formation from [2-(14)C]glucose or [U-(14)C]-glucose the effect not being wholly due to isotopic dilution. 6. Acetoacetate inhibits non-competitively the oxidation of [1-(14)C]pyruvate, the effect being attributed to competition between acetyl-CoA and CoA for the pyruvate-oxidation system. 7. Acetoacetate increases the rate of aerobic formation of lactate from glucose with both adult and infant rat brain slices. 8. The presence of 0.1mm-2,4-dinitrophenol diminishes but does not abolish the rate of (14)CO(2) formation from [3-(14)C]acetoacetate in rat brain slices. This points to the participation of ATP in the process of oxidation of acetoacetate in infant or adult rat brain. 9. The presence of 5mm-d-glutamate inhibits the rate of (14)CO(2) formation from [3-(14)C]acetoacetate, in the presence or absence of glucose. 10. Labelled amino acids are formed from [3-(14)C]acetoacetate in both adult and infant rat brain-cortex slices, but the amounts are smaller than those found with [2-(14)C]glucose in adult rat brain and greater than those found with [2-(14)C]glucose in infant rat brain. 11. Acetoacetate is not as effective as glucose as a precursor of acetylcholine in adult rat brain but is as effective as glucose in infant rat brain slices. 12. Acetoacetate or beta-hydroxybutyrate is a more potent source of acetyl-CoA than is glucose in infant rat brain slices but is less so in adult rat brain slices.

The role of lipids in membrane transport in Mycoplasma laidlawii.

AbstractPulse labeling of metabolizing cells ofMycoplasma laidlawii, strain B with14C‐glucose results in rapid turnover of the glucose moiety in carotenyl glucoside and phosphatidyl glucose. Pulse labeling also occurs in the fatty acid radicals of carotenyl esters. No labeling of phosphatidyl glycerol, carotenol or monoglucosyl diglyceride occurs. No turnover of14C occurs in diglucosyl diglyceride. Rapid turnover of32P in phosphatidyl glucose, but not in phosphatidyl glycerol, also occurs. The rate of14CO2 evolution is equivalent to the rate of disappearance of14C in total lipids of cells prelabeled with14C‐glucose. β‐Glucosidase inhibition results in inhibition of glucose utilization. The reverse effect is not seen. A theory involving lipids as carriers in the transport of glucose into the cell and acetate, the end product of glucose metabolism, out of the cell is presented. This theory is compatible with known information concerning membrane structure, membrane transport and metabolism in Mycoplasmas.