INORGANIC CARBON AND ACETATE ASSIMILATION IN BOTRYOCOCCUS BRAUNII(CHLOROPHYTA)1

Assimilation of ¹⁴CO₂ or ¹⁴C-acetate by the hydrocarbon producing alga Botryococcus braunii Kützing was investigated to determine the allocation of incorporated ¹⁴C among early metabolites of photosynthesis and secondary metabolites. When the cells were exposed to NaH¹⁴CO₃ for 10 sec, over 90% of incorporated ¹⁴C was detected in phosphoglycerate, suggesting that this alga assimilates inorganic carbon by the C-3 pathway. The distribution pattern of ¹⁴C in the number of metabolites revealed that organic acids, neutral sugars and amino acids were first labelled with ¹⁴C, and, after lag periods of a few minutes, lipids including hydrocarbon were increasingly labelled. Addition of 5 mM acetate to the culture medium did not affect the growth of this alga but enhanced cellular respiration. The incorporation of ¹⁴CO₂ into the lipid fraction was stimulated, but net photosynthesis was inhibited by the addition of acetate. ¹⁴C-acetate was incorporated into lipids at a very low rate in comparison with the rate of ¹⁴CO₂ incorporation.     

Enhanced Dark CO(2) Fixation by Preilluminated Chlorella pyrenoidosa and Anacystis nidulans

The products of short time photosynthesis and of enhanced dark ¹⁴CO₂ fixation (illumination in helium prior to addition of ¹⁴CO₂ in dark) by Chlorella pyrenoidosa and Anacystis nidulans were compared. Glycerate 3-phosphate, phosphoenolpyruvate, alanine, and aspartate accounted for the bulk of the ¹⁴C assimilated during enhanced dark fixation while hexose and pentose phosphates accounted for the largest fraction of isotope assimilated during photosynthesis. During the enhanced dark fixation period, glycerate 3-phosphate is carboxyl labeled and glucose 6-phosphate is predominantly labeled in carbon atom 4 with lesser amounts in the upper half of the C₆ chain and traces in carbon atoms 5 and 6. Tracer spread throughout all the carbon atoms of photosynthetically synthesized glycerate 3-phosphate and glucose 6-phosphate. During the enhanced dark fixation period, there was a slow formation of sugar phosphates which subsequently continued at 5 times the initial rate long after the cessation of ¹⁴CO₂ uptake. To explain the kinetics of changes in the labelling patterns and in the limited formation of the sugar phosphates during enhanced dark CO₂ fixation, the suggestion is made that most of the reductant mediating these effects did not have its origin in the preillumination phase.

It is concluded that a complete photosynthetic carbon reduction cycle operates to a limited extent, if at all, in the dark period subsequent to preillumination.

     

Glycolic Acid Labeling During Photosynthesis with CO(2) and Tritiated Water

Chlorella pyrenoidosa were allowed to photosynthesize for short periods of time in the presence of ¹⁴CO₂ and HTO. Analysis of tritium and ¹⁴C labeling of photosynthetic intermediate compounds showed that the T/¹⁴C ratio of glycolic acid was comparable to that of intermediate compounds of the photosynthetic carbon reduction cycle when photosynthesis was performed in nearly 100% oxygen and only slightly higher under steady-state conditions. It is concluded that formation of labeled glycolic acid as a consequence of its proposed hydrogen transport role in photosynthesis is quantitatively of limited importance compared to the net synthesis of glycolic acid from CO₂.     

Oxygen effect on photosynthetic and glycolate pathways in young maize leaves

To study the effect of O₂ on the photosynthetic and glycolate pathways, maize leaves were exposed to ¹⁴CO₂ during steady-state photosynthesis in 21 or 1% O₂. At the two O₂ concentrations after a ¹⁴CO₂ pulse (4 seconds) followed by a ¹²CO₂ chase, there was a slight difference in CO₂ uptake and in the total amount of ¹⁴C fixed, but there were marked changes in ¹⁴C distribution especially in phosphoglycerate, ribulose bisphosphate, glycine, and serine. The kinetics of ¹⁴C incorporation into glycine and serine indicated that the glycolate pathway is inhibited at low O₂ concentrations. In 1% O₂, labeling of glycine was reduced by 90% and that of serine was reduced by 70%, relative to the control in 21% O₂. A similar effect has been observed in C₃ plants, except that, in maize leaves, only 5 to 6% of the total ¹⁴C fixed under 21% O₂ was found in glycolate pathway intermediates after 60 seconds chase. This figure is 20% in C₃ plants. Isonicotinyl hydrazide did not completely block the conversion of glycine to serine in 21% O₂, and the first carbon atom of serine was preferentially labeled during the first seconds of the chase. These results supported the hypothesis that the labeled serine not only derives from glycine but also could be formed from phosphoglycerate, labeled in the first carbon atom during the first seconds of photosynthesis.     

Effect of Oxygen Concentration on C-Photoassimilate Transport from Leaves of Salvia splendens L

Partitioning and transport of recently fixed photosynthate was examined following ¹⁴CO₂ pulse-labeling of intact, attached leaves of Salvia splendens L. maintained in an atmosphere of 300 microliters per liter CO₂ and 20, 210, or 500 milliliters per liter O₂. Under conditions of increasing O₂ (210, 500 milliliters per liter), a smaller percentage of the recently fixed ¹⁴C in the leaf was allocated to starch, whereas a greater percentage of the fixed ¹⁴C appeared in amino acids, particularly serine. The increase in ¹⁴C in amino acids was reflected in material exported from source leaves. A higher percentage of ¹⁴C in serine, glycine, and glutamate was recovered in petiole extracts when source leaves were maintained under elevated O₂ levels. Although pool sizes of these amino acids were increased in both the leaves and petioles with increasing photorespiratory activity, no significant changes in either ¹⁴C distribution or concentration of transport sugars (i.e. stachyose, sucrose, verbascose) were observed. The data indicate that, in addition to being recycled intracellularly into Calvin cycle intermediates, amino acids produced during photorespiration may also serve as transport metabolites, allowing the mobilization of both carbon and nitrogen from the leaf under conditions of limited photosynthesis.     

Continuous measurement of 14C-labeled carbon dioxide and lactic acid by cultured cells grown in Leighton tubes.

A procedure for continuous measurement of ¹⁴CO₂ production by cultured cells grown in Leighton tubes has been described. The apparatus developed also permits aliquots of the incubation medium to be taken during the experiments for analysis of labeled metabolites released into the solution. A simple method for determination of [¹⁴C]lactic acid in such aliquots has been described. The reproducibility and usefulness of the apparatus has been demonstrated by incubating fibroblasts with glucose labeled in the C-1 or C-6 position, and examining the effects of selected drugs on CO₂ and lactic acid production.     

Sul Metabolismo Dell'Alcool Etilico in Tessuti Di Fusto Di « Pisum »

Abstract

On the metabolism of ethanol in the Pea stem tissues. — The average concentration of ethanol in the growing part of the etiolated pea internodes is of the order of 10^-3M. Previous work showed that auxin at growth promoting concentration markedly lowers this level in the excised internodes. This finding prompted a series of investigations on C¹⁴ labeled ethanol utilization in this material.

The capacity of the segments to metabolize ethanol is remarkable: with an external ethanol concentration 5X10^-3M the C¹⁴ labeled CO₂ originated from 1-C¹⁴ ethanol accounted for about 10% of total CO₂ produced during the first hour of treatment. Moreover, an amount of ethanol about 10 fold higher that that dissimilated to CO₂ was metabolized to various yet unidentified compounds. The ratio between the contribution of ethanol to CO₂ and that to other metabolites appeared maximal in the first period after feeding the labeled compound. This ratio was significantly higher then that found for 6-C¹⁴ glucose.

These preliminary results suggest the possibility that ethanol produced in glycolysis could represent an interesting metabolite in an anabolic pathway different from the one leading from pyruvate to the Krebs cycle acids.     

Photosynthetic products of division synchronized cultures of euglena

Rates and products of photosynthetic ¹⁴CO₂ fixation by division synchronized cultures of Euglena gracilis strain Z were determined over the cycle. Rate of ¹⁴CO₂ fixation doubled in a continuous manner throughout the light phase followed by a slight reduction of photosynthetic capacity in the dark phase. Greater ¹⁴C incorporation into the nucleic acid-polysaccharide fraction occurred with mature cells. Products of ¹⁴CO₂ fixation varied markedly over the cycle: although with mature cells ¹⁴C-labeled sucrose was not detected, with dividing cells this was the main sugar labeled; in young cells ¹⁴C maltose was formed. Cells removed at end of dark phase accumulated ¹⁴C in glycolate, whereas at other stages over the cycle less ¹⁴C was present in glycolate, and this was accompanied by a rapid incorporation of ¹⁴C into glycine and serine. Glycerate was an early and major product of photosynthesis with cells at the mature stage of the cycle.     

Veränderliche Markierungsmuster bei14CO2-Fütterung vonBryophyllum tubiflorum zu verschiedenen Zeitpunkten der Hell/Dunkelperiode

Summary Detached phyllodia ofBryophyllum tubiflorum were fed under illumination with¹⁴CO₂ at different times during the light/dark period (12:12 hours). After photosynthesis in presence of¹⁴CO₂ during the intrinsic dark period the greatest part of soluble radioactivity was found in malate. When the same experiment was repeated during the light period, radioactivity was incorporated mainly into sucrose in the first hours while malate was labelled rather weakly. In the late afternoon (last third of the light period), malate became most heavily labelled again during photosynthesis with¹⁴CO₂.Our results indicate that the synthesis of malate by PEP-carboxylase/malate dehydrogenase is inhibited at certain times during the night/day period by end product inhibition of PEP-carboxylase, as was demonstrated byQueiroz (1967, 1968) andTing (1968) in vitro.During inhibition of the PEP-carboxylase there is no competition between the synthesis of malate and CO₂-fixation by the Calvin cycle. Thus radioactivity can flow into sucrose via the Calvin cycle during this time. When the malate content of the phyllodia is low, CO₂-fixation by PEP-carboxylase is not inhibited. Now this pathway dominates over photosynthesis via the Calvin cycle, for PEP-carboxylase has a higher affinity for CO₂ than carboxydismutase. Therefore malate now becomes more labelled than sucrose.     

A method for continuous measurement of export from a leaf

Export of labeled material derived by continuous photosynthesis in ¹⁴CO₂ was monitored with a Geiger-Müller detector positioned next to an exporting leaf blade. Rate of export of labeled material was calculated from the difference between rates of retention and net photosynthesis of labeled carbon for the observed leaf. Given certain conditions, including nearly constant distribution of labeled material among minor veins and various types of cells, count rate data for the source leaf can be converted to rate of export of carbon. Changes in counting efficiency resulting from changes in leaf water status can be corrected for with data from a transducer which measures leaf thickness.     

Light-Dark Transients in Levels of Intermediate Compounds during Photosynthesis in Air-Adapted Chlorella

The labeling of intermediate compounds and photosynthetic cofactors during photosynthesis and periods of darkness by Chlorella pyrenoidosa in the presence of ³²P-labeled phosphate and ¹⁴CO₂ have heen investigated. Algae adapted to photosynthesis in air were used, and the level of carbon dioxide was maintained at approximately 0.04 % and at constant specific radioactivity during the course of the experiments. The transient changes which occur in the levels of labeled fructose-1,6-diphosphate and in sedoheptulose-1,7-diphosphate, and in the corresponding monophosphates when the light is turned off suggest a light activation of the diphosphatase enzymes which decays after about 2 minutes of darkness. It is suggested that a light-dark switch in enzymic activities permits photosynthesis and glycolysis to occur in light and dark respectively with the same enzymic apparatus. The greatly diminished rate of disappearanec of the carboxylation substrate, ribulose-1,5-diphosphate, after about 2 minutes suggests that there is also a light activation of the carboxylation reaction in vivo. Large transient changes in the level of pyrophosphate between light and dark indicate that there may be an unstable cofactor which decomposes to give pyrophosphate during or alter killing of the algal cells. The possibility that this cofactor is involved in an activation of Carbon dioxide for the carboxylation reaction in vivo is suggested. Light-dark transient changes in labeling of other compounds of the photosynthetic carbon reduction cycle and related compounds were determined, and possible significance of these changes is discussed.(PDF DAMAGED)     

Leaflet photosynthesis rate and carbon metabolite accumulation patterns in nitrogen-limited, vegetative soybean plants

Prolonged inorganic nitrogen (NO₃ ^–+NH₄ ⁺) limitation of non-N₂-fixing soybean plants affected leaflet photosynthesis rates, photosynthate accumulation rates and levels, and anaplerotic carbon metabolite levels. Leaflets of nitrogen-limited (N-Lim), 27–31-day-old plants displayed 15 to 23% lower photosynthesis rates than leaflets of nitrogen-sufficient (N-Suff) plants. In contrast, N-Lim plant leaflets displayed higher sucrose and starch levels and rates of accumulation, as well as higher levels of carbon metabolites associated with sucrose and starch synthesis, e. g., glycerate-3-phosphate and glucose phosphates, than N-Suff plant leaflets. Concurrently, levels of soluble protein, chlorophyll, and anaplerotic metabolites, e.g., malate and phosphoenolpyruvate, were lower in leaflets of N-Lim plants than N-Suff plants, suggesting that the enzymes of the anaplerotic carbon metabolite pathway were lower in activity in N-Lim plant leaflets. Malate net accumulation rates in the earliest part of the illumination period were lower in N-Lim than in N-Suff plant leaflets; however, by the midday period, malate accumulation rate in N-Lim plant leaflets exceeded that in leaflets of N-Suff plants. Further, soluble protein accumulation rates in leaflets of N-Suff and N-Lim plants were similar, and the rate of dark respiration, measured in the early part of the dark period, was higher in N-Lim plant leaflets than in N-Suff plant leaflets. It was concluded that during prolonged N-limitation, foliar metabolite conditions favored the channelling of a large proportion of the carbon assimilate into sucrose and starch, while assimilate flow through the anaplerotic pathway was diminished. However, in some daytime periods, there was a normal level of carbon assimilate channelled through the anaplerotic pathway for ultimate use in amino acid and protein synthesis.Abbreviations ADPG-PPiase ADPglucose pyrophosphorylase - Ce CO₂ in the leaf photosynthesis measuring cuvette - Ci leaf internal CO₂ during photosynthesis measurement - Chl chlorophyll - DHAP dihydroxyacetone phosphate - GAP glyceraldehyde-3-phosphate - G_sw stomatal conductance with units as mmol H₂O m^–2 s^–1 - G1P glucose-1-phosphate - G6P glucose-6-phosphate - F6P fructose-6-phosphate - FBP fructose-1,6-bisphosphate - FBPase-pH 8.1 chloroplastic fructose-1,6-bisP (C-1) phosphatase (pH 8.1) - MAL malate - N inorganic nitrogen, i.e. NO₃ ^–+NH₄ ⁺ (at levels and molar ratios indicated) - PE post-emergence - PEP phosphoenolpyruvate - PEPCase phosphoenolpyruvate carboxylase - PGA 3-phosphoglycerate - PYR pyruvate - PYR kinase pyruvate kinase - Pn net CO₂ photoassimilation in leaves - PPFD photosynthetic photon flux density - PPRC pentose phosphate reductive cycle - RuBP ribulose-1,5-bisphosphate; rubisco-ribulose-1,5-bisphosphate carboxylase/oxygenase - SLW specific leaf mass - SPS sucrose-6-phosphate synthase - TCA cycle tricarboxylic acid cycle; triose-P-DAP+GAP     

Translocation: EFFLUX OF SUGARS ACROSS THE PLASMALEMMA OF MESOPHYLL PROTOPLASTS

During photosynthesis by mesophyll protoplasts of wheat and tobacco, a linear efflux of sucrose and hexoses to the medium was observed, with the size of the intraprotoplast sugar pools remaining constant. Efflux of metabolites labeled by ¹⁴CO₂ fixation was initially low because of dilution by internal pools, but increased exponentially with time. The results have significance both in terms of the mechanism of translocation and the use of isolated protoplasts in photosynthetic studies.     

PHOTOSYNTHESIS AND CALCIFICATION BY EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) AS A FUNCTION OF INORGANIC CARBON SPECIES

To test the possibility of inorganic carbon limitation of the marine unicellular alga Emiliania huxleyi (Lohmann) Hay and Mohler, its carbon acquisition was measured as a function of the different chemical species of inorganic carbon present in the medium. Because these different species are interdependent and covary in any experiment in which the speciation is changed, a set of experiments was performed to produce a multidimensional carbon uptake scheme for photosynthesis and calcification. This scheme shows that CO₂ that is used for photosynthesis comes from two sources. The CO₂ in seawater supports a modest rate of photosynthesis. The HCO is the major substrate for photosynthesis by intracellular production of CO₂ (HCO+ H⁺→ CO₂+ H₂O → CH₂O + O₂). This use of HCO is possible because of the simultaneous calcification using a second HCO, which provides the required proton (HCO+ Ca²⁺→ CaCO₃+ H⁺). The HCO is the only substrate for calcification. By distinguishing the two sources of CO₂ used in photosynthesis, it was shown that E. huxleyi has a K_½ for external CO₂ of “only” 1.9 ± 0.5 μM (and a V_max of 2.4 ± 0.1 pmol·cell⁻¹·d⁻¹). Thus, in seawater that is in equilibrium with the atmosphere ([CO₂]= 14 μM, [HCO]= 1920 μM, at fCO₂= 360 μatm, pH = 8, T = 15° C), photosynthesis is 90% saturated with external CO₂. Under the same conditions, the rate of photosynthesis is doubled by the calcification route of CO₂ supply (from 2.1 to 4.5 pmol·cell⁻¹·d⁻¹). However, photosynthesis is not fully saturated, as calcification has a K_½ for HCO of 3256 ± 1402 μM and a V_max of 6.4 ± 1.8 pmol·cell⁻¹·d⁻¹. The H⁺ that is produced during calcification is used with an efficiency of 0.97 ± 0.08, leading to the conclusion that it is used intracellularly. A maximum efficiency of 0.88 can be expected, as NO uptake generates a H⁺ sink (OH⁻ source) for the cell. The success of E. huxleyi as a coccolithophorid may be related to the efficient coupling between H⁺ generation in calcification and CO₂ fixation in photosynthesis.     

Analysis of steady state photosynthesis in alfalfa leaves

A method for carrying out kinetic tracer studies of steady state photosynthesis in whole leaves has been developed. An apparatus that exposes whole leaves to ¹⁴CO₂ under steady state conditions, while allowing individual leaf samples to be removed as a function of time, has been constructed. Labeling data on the incorporation of ¹⁴C into Medicago sativa L. metabolite pools are reported. A carbon dioxide uptake rate of 79 micromoles ¹⁴CO₂ per milligram chlorophyll per hour was observed at a CO₂ level slightly below that of air. Several actively turning over pools of early and intermediate metabolites, including 3-phosphoglyceric acid, glycerate, citrate, and uridine diphosphoglucose, showed label saturation after approximately 10 to 20 minutes of photosynthesis with ¹⁴CO₂ under steady state conditions. Alanine labeling increased more rapidly at first, and then at a lower rate as saturation was approached. Sucrose was a major product of photosynthesis and label saturation of the sucrose pool was not observed. Labeled carbon appeared rapidly in secondary metabolites. The steady state apparatus used has numerous advantages, including leaf temperature control, protection against leaf dehydration, high illumination, known ¹⁴CO₂ specific radioactivity, and provision for control and adjustment of ¹⁴CO₂ concentration. The apparatus allows for experiments of long duration and for sufficient sample points to define clearly the metabolic steady state.     

Pod photosynthesis and seed dark CO2 fixation support oil synthesis in developingBrassica seeds

Rate of photosynthesis and activities of photosynthetic carbon reduction cycle enzymes were determined in pods (siliqua), whereas rate of dark CO₂ fixation, oil content and activities of enzymes involved in dark CO₂ metabolism were measured in seeds ofBrassica campestris L. cv. Toria at different stages of pod/seed development. The period between 14 and 35 days after anthesis corresponded to active phase of seed development during which period, seed dry weight and oil content increased sharply. Rate of pod photosynthesis and activities of photosynthetic carbon reduction cycle enzymes were maximum in younger pods but sufficiently high levels were retained up to 40 days after anthesis. The rate of dark¹⁴CO₂ fixation in seeds increased up to 21 days after anthesis and declined thereafter but maintaining sufficiently high rates till 35 days after anthesis. Similarly various enzymes viz., phosphoenolpyruvate carboxylase, NAD⁺-malate dehydrogenase and NADP⁺-malic enzyme, involved in dark CO₂ metabolism retained sufficient activities during the above period. These enzyme activities were more than adequate to maintain the desired supply of malate which mainly arises from dark CO₂ fixation in seeds and further translocated to leucoplasts for onward synthesis of fatty acids. Enzyme localization experiments revealed phosphoenolpyruvate carboxylase and enzymes of sucrose metabolism to be present only in cytosol, whereas enzymes of glycolysis were present both in cytosolic and leucoplastic fractions. These results indicated that oil synthesis in developingBrassica seeds is supported by pod photosynthesis and dark CO₂ fixation in seeds as the former serves as the source of sucrose and the latter as a source of malate     

Aminooxyacetate stimulation of glycolate formation and excretion by chlamydomonas

Aminooxyacetate (1 millimolar) did not inhibit photosynthetic ¹⁴CO₂ fixation by Chlamydomonas reinhardtii Dangeard, (−) strain (N.90) but greatly stimulated the biosynthesis and excretion of glycolate. Similar results were obtained from cells grown with 5% CO₂ or low CO₂ (air). After 2 minutes with air-grown cells, [¹⁴C]glycolate increased from 0.3% of the total ¹⁴C fixed by the control to 11.7% in the presence of aminooxyacetate and after 10 minutes from 3.8% to 41.1%. Ammonium nitrate (0.2 millimolar) in the media blocked the aminooxyacetate stimulation of glycolate excretion. Chromatographic analyses of the labeled products in the cells and supernatant media indicated that aminooxyacetate also completely inhibited the labeling of alanine while some pyruvate accumulated and was excreted. A high percentage (35%) of initial ¹⁴CO₂ fixation was into C₄ acids. Initial products of ¹⁴CO₂ fixation included phosphate esters as well as malate, aspartate, and glutamate in treated or untreated cells. Lactate was also a major early product of photosynthesis, and its labeling was reduced by aminooxyacetate. Inasmuch as lactate was not excreted, glycolate excretion seemed to be specific. When photosynthesis was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, labeled organic and amino acids but not phosphate esters were lost from the cells. Aminooxyacetate did not inhibit the enzymes associated with glycolate synthesis from ribulose bisphosphate.     

The incorporation of nitrogen into products of recent photosynthesis in Anabaena cylindrica Lemm.

In vivo tracer studies with ¹⁴C have been performed to help determine pathways of incorporation of newly assimilated nitrogen into N₂-fixing cells of Anabaena cylindrica. After photosynthesis in Ar:O₂:¹⁴CO₂ for 30 min, the addition of N₂ or NH ₄ ⁺ resulted in increased rates of ¹⁴CO₂-incorporation both in the light and dark, and in increased incorporation of ¹⁴C into amino acids at the expense of sucrose and sugar phosphates. Evidence of enhanced sucrose catabolism and increased pyruvate kinase activity was obtained on adding nitrogen, and, of the ¹⁴C-labelling entering the tricarboxylic acid cycle, more appeared in citrate and 2-oxoglutarate than in malate and oxaloacetate. The kinetics of ¹⁴C-incorporation into various amino acids suggest that in the light and dark the most important route of primary ammonia assimilation involves glutamine synthetase and that glutamate, aspartate, glycine and probably alanine are formed secondarily from glutamine.     

METABOLISM OF MALONIC ACID IN RAT BRAIN AFTER INTRACEREBRAL INJECTION

Labeled malonic acid ([1-¹⁴C] and [2-¹⁴C]) was injected into the left cerebral hemisphere of anesthetized adult rats in order to determine the metabolic fate of this dicarboxylic acid in central nervous tissue. The animals were allowed to survive for 2, 5, 10. 15 or 30min. Blood was sampled from the torcular during the experimental period and labeled metabolites were extracted from the brain after intracardiac perfusion. There was a very rapid efflux of unreacted malonate in the cerebral venous blood. Labeled CO₂ was recovered from the venous blood and the respired air after the injection of [1-¹⁴C]malonate but not after [2-¹⁴C]malonate. The tissue extracts prepared from the brain showed only minimal labeling of fatty acids and sterols. Much higher radioactivity was present in glutamate, glutamine, aspartate, and GABA. The relative specific activities (RSA) of glutamine never rose above 1.00. Aspartate was labeled very rapidly and revealed evidence of ¹⁴CO₂ fixation in addition to labeling through the Krebs cycle. GABA revealed higher RSA after [1-¹⁴C]malonate than after [2-¹⁴C]malonate. Sequential degradations of glutamate and aspartate proved that labeling of these amino acids occurred from [1-¹⁴C] acetyl-CoA and [2-¹⁴C] acetyl-CoA, respectively, via the Krebs cycle. Malonate activation and malonyl-CoA decarboxylation in vivo were similar to experiments with isolated mitochondria. However, labeled malonate was not incorporated into the amino acids of free mitochondria. The results were compared to data obtained after intracerebral injection of [1-¹⁴C]acetate and [2-¹⁴C]acetate.     

Isotopic studies of carbohydrate metabolism during basidiospore germination in Schizophyllum commune

Summary The metabolism and fate of specifically labeled glucose-¹⁴C were compared to mannitol-l-¹⁴C and arabitol-l-¹⁴C during basidiospore germination of Schizophyllum commune on glucose-asparagine minimal broth. Glucose-l-¹⁴C metabolism led to more ¹⁴CO₂ evolution than glucose-6-¹⁴C in spores and the former activity increased upon germination. Liberation of ¹⁴CO₂ from glucose-3,4-¹⁴C increased at 8 h to 12 h of germination and exceeded the amount of radioactive ¹⁴CO₂ released from glucose-1-¹⁴C. The ¹⁴CO₂ released from glucose-2-¹⁴C increased continually during germination while only minor changes in ¹⁴CO₂ evolution occurred with glucose-6-¹⁴C. Unlabeled ethanol (0.25 M) inhibited ¹⁴CO₂ evolution with glucose-3,4-¹⁴C and ungerminated spores and this inhibition disappeared upon germination.More ¹⁴CO₂ was evolved from labeled glucose during germination and less radioactivity became associated with cellular material. Of the latter, alcohol-soluble extracts of spores or germlings contained mainly radioactive trehalose, less mannitol and little or no labeled arabitol, and this decreased upon germination. Germlings also converted more radioactive glucose-¹⁴C into KOH-insoluble material and KOH-soluble components. Spores or germlings converted arabitol-1-¹⁴C primarily into trehalose and this was not the case for mannitol-1-¹⁴C.