MASS MORTALITY OF MARINE AND ESTUARINE FISH IN THE SWARTVLEI AND WILDERNESS LAKE SYSTEMS,SOUTHERN CAPE.

Summary

Two incidences of mass mortality of fish were recorded in two saline waterbodies (Swartvlei estuary and Rondevlei) in the Wilderness National Park. Species affected were the Knysna seahorse (Hippocampus capensis) and longsnout pipefish (Syngnathus acus) in the Swartvlei estuary, and Cape stumpnose (Rhabdosargus holubi) and white steenbras (Lithognathus lithognathus) in Rondevlei. Comparison of water quality parameters during fish mortalities to past ranges and reported species tolerances indicated that the probable causes for the mortalities were high water temperature in the Swartvlei estuary, and low dissolved oxygen concentration in Rondevlei.     

Glucose Metabolism in Sediments of a Eutrophic Lake: Tracer Analysis of Uptake and Product Formation

The uptake of glucose and the formation of end products from glucose catabolism have been measured for sediments of eutrophic Wintergreen Lake with a combination of tritiated and ¹⁴C-labeled tracers. Time course analyses of the loss of [³H]glucose from sediments were used to establish rate constants for glucose uptake at natural substrate concentrations. Turnover times from these analyses were about 1 min for littoral and profundal sediments. No seasonal or site differences were noted in turnover times. Time course analyses of [U-¹⁴C]glucose uptake and ¹⁴C-labeled end product formation indicated that glucose mass flow could not be calculated from end product formation since the specific activity of added [¹⁴C]glucose was significantly diluted by pools of intracellular glucose and glucose metabolites. Mass flow could only be accurately estimated by use of rates of uptake from tracer studies. Intermediate fermentation end products included acetate (71%), propionate (15%), lactate (9%), and only minor amounts of butyrates or valerates. Addition of H₂ to sediments resulted in greater production of lactate (28%) and decreased formation of acetate (50%), but did not affect glucose turnover. Depth profiles of glucose uptake indicated that rates of uptake decreased with depth over the 0- to 18-cm interval and that glucose uptake accounted for 30 to 40% of methanogenesis in profundal sediments.     

Aerobic and anaerobic metabolism in Entamoeba histolytica

Respiration by Entamoeba histolylica is confirmed. A doubling of the rate of oxygen uptake was observed upon the addition of d-glucose to cells in which the glycogen reserve had been partially depleted. In cells metabolizing endogenous substrates the rate of oxygen uptake was not influenced by sodium cyanide or sodium succinate. It was slightly depressed when d-mannose was the added sugar. The end products, CO₂, ethanol, and acetate accounted for essentially all of the glucose carbon utilized in both aerobic and anaerobic experiments. The radioactivity from uniformly labelled ¹⁴C-glucose was found in these products. Three times as much ethanol as acetate was produced in the anaerobic experiments and in the aerobic experiments this ratio was approximately reversed.     

Preferential Utilization of Cellobiose by Thermomonospora curvata

Thermomonospora curvata was cultivated on mineral salts medium containing glucose and cellobiose under conditions that increasingly favored the uptake of glucose. In each case cellobiose was utilized in preference to glucose and induced β-glucosidase and endoglucanase activity. [¹⁴C]glucose metabolism studies indicated that cellobiose was not cleaved by extracellular β-glucosidase and transported as glucose. No evidence of cellobiose phosphorylase or a cellobiose-specific phosphoenolpyruvate-phosphotransferase system was observed.     

Investigations on the mode of action of sodium N-methyldithiocarbamate in Fusarium oxysporum f. sp. lycopersici

Summary A radiorespirometric technique was used to determine the effects of sodium N-methyldithiocarbamate (NaMDC) on uptake and oxidation of glucose by Fusarium oxysporum f. sp. lycopersici. The principal glucose oxidation pathway of the fungus was found to be the pentose cycle. Shifts to other oxidation pathways were not significant even when the fungus was treated with extremely high concentrations of NaMDC (5×10^-2 M). Only when zinc ions were added to NaMDC solutions were shifts in pathway (and a drastic increase in toxicity) noted. The main effect of NaMDC was to delay the complete oxidation of glucose to CO₂. In the concentration range between 0.5 to 10.0×10^-2 M NaMDC dose response curves were bimodal with respect to spore germination, colony development, and CO₂ production; with respect to glucose uptake the curves were unimodal. The bimodal dosage response curves could be divided into a first zone of inhibition, a zone of reversed toxicity, and a second zone of inhibition. Within the first zone of inhibition, colony development proved to be more sensitive to NaMDC than spore germination. In the zone of reversed toxicity the incorporation of carbon into the spores drops sharply, while in the second zone of inhibition a strong inhibition of glucose uptake is the dominating effect. It is indicated that NaMDC interfers with biosynthetic activities rather than enzymes of catabolic pathways.List of abbreviations NaMDC Sodium N-methyldithiocarbamate - NaDMDC Sodium dimethyldithiocarbamate - TMTD Tetramethylthiuram disulfide, [=Bis(dimethylthiocarbamyl)disulfid, Thiram^®] - DMTD N,N-dimethylthiuram disulfide [=Bis-(methylthiocarbamyl)disulfid] - MIT Methylisothiocyanate     

PHOSPHORUS DYNAMICS IN THE MONIMOLIMNION OF SWARTVLEI

SUMMARY

The exchange of phosphorus between the bottom sediment and monimolimnion of Swartvlei, a meromictic, humic lake, was investigated during the last three months of 1980. The concentrations of oxygen, dissolved salts, phosphorus and Fe⁺⁺ in the water column were monitored, and electrode potentials in the bottom mud were measured, at approximately weekly intervals. At the same time laboratory experiments were performed, using Jenkin core samples, to observe the effect of changing oxygen concentration and salinity on phosphate exchange between sediment and water, and on electrode potentials at the sediment-water interface. Phosphorus was released under unaerobic conditions at a rate of 2,5 mg P m^?2 d^?1 and was taken up again under aerobic conditions at 1,6 mg P m^?2 d^?1 These values were in agreement with existing observed data on changes in phosphate concentration.     

Effects of low water potentials on respiration and on glucose and acetate uptake,by Chlorella pyrenoidosa

Summary Chlorella pyrenoidosa was subjected to a range of water potentials and the effects of these treatments on endogenous respiration and on the uptake and respiration of glucose and acetate were measured.For a given water potential the reductions were greatest for glucose, less for acetate, and least for endogenous respiration. At intermediate water potentials of about-10 atm, glucose respiration was depressed strongly at first, but this respiration approached control levels after two to three hours at low water potentials.The reduced respiration of substrates was caused by inhibition of glucose and acetate uptake, as demonstrated by ¹⁴C uptake experiments over short periods. These effects on uptake are attributed to low water potentials, rather than to any possible competition between the molecules of the osmotica and the substrates. Evidence for this view includes the equal inhibitions of glucose-induced respiration by osmotica with such diverse molecular structure as mannitol, KCl, and polyethylene glycol 1540. More conclusively, glucose itself was used as an osmotic agent and its inhibition of glucose-induced respiration was very similar to that by mannitol solutions of equal water potentials.Respiratory activity was much less reduced than uptake. This was demonstrated by lowering the water potential of cells which had already absorbed glucose from a control medium. The subsequent respiration was much higher than that for cells continuously exposed to low water potential.The findings are discussed in relation to the reduced transport of ions and sucrose, which is known to occur in vascular plants subjected to a water stress.The results demonstrate the advantages of using a unicellular organism in the study of metabolic effects of water deficits in plants.     

AMINO ACID METABOLISM IN GLIAL CELLS: HOMEOSTATIC REGULATION OF INTRA- and EXTRACELLULAR MILIEU BY C-6 GLIOMA CELLS

Abstract— The amino acid and carbohydrate metabolism of confluent cultures of C-6 glioma cells has been investigated. It was observed that the presence of glutamine in the incubation fluid was essential to maintain high glutamine levels in the cells during a 2 h incubation. When cells were incubated in a cerebrospinal fluid-like medium glutamate, glutamine, aspartate and γ-aminobutyrate (GABA) levels were comparable to those occurring in whole forebrain of adult rat in vivo. Glucose uptake was high, approx 1 μmol/mg protein/2 h, 50% of which was accounted for by lactate production. Of the remaining glucose uptake a substantial proportion was unaccounted for by known oxygen-coupled citric acid cycle flux, or glycogen or amino acid synthesis. Interestingly, the cells released into the medium significant amounts of the neuroinhibitory amino acids, GABA and glycine, and rapidly cleared the medium of the neuroexcitatory amino acids glutamate and aspartate. Metabolism of [2-¹⁴C]glucose and [³H]acetate by the cells indicated rapid labelling of the glutamate and aspartate pools of the cells by glucose in 1 h, but the relative specific activities of glutamine and GABA were much lower. The metabolism of tracer concentrations of [³H]acetate to glutamate by the cells indicated greater dilution of this isotope compared to that of labelled glucose. However, the ratio of ³H to ¹⁴C radioactivity in glutamate and other amino acids was similar to that in the mixture of glucose and acetate added to the medium. Therefore, some active route of acetate metabolism which communicates metabolically with the route of glucose metabolism to glutamate appears to exist in the cells. Significant acetate activation and fatty acid turnover would explain the present results. Some of the amino acid labelling patterns observed in these studies are not consistent with these glial-like cells behaving as models for the small compartment of amino acid metabolism in brain. Enzyme measurements corroborated the metabolic studies. Glutamate decarboxylase activity was 3–10% of the level found in whole brain. GABA transaminase was also low compared to brain as was glutamine synthetase. Glutamate dehydrogenase was present at levels equal to or higher than those of whole brain.     

Primary productivity of the upper reaches of a South African estuary (Swartvlei)

Primary productivity, using the ¹⁴C technique was measured in the expanded lake-like upper reaches of a South African estuary during 1972. Maximal assimilation per unit volume ranged between 5.0 and 13.1 mg C m^?3 h^?1 and areal productivity ranged between 13.1 and 36.9 mg C m^?2 h^?1. For most of the period the euphotic zone (level of 1% of surface light) extended to only 4.5 m. The poor light conditions in the estuary were due to the heavy content of humic material and suspended detrital matter. Light, therefore, was a major factor limiting primary productivity. The PO₄-P concentration reached an undetectable level following a large diatom increase and nutrient limitation may have occurred. The phytoplankton population of the upper reaches of Swartvlei was dominated by nannoplanktonic (< 60 μm) diatoms and dinoflagellates. The ecological advantages that these small organisms might have in an environment such as Swartvlei are discussed.     

Substrate Utilization by Suspension Cultures and Somatic Embryos of Daucus carota L. Measured by C NMR

The uptake and utilization of sucrose by embryogenic suspension cultures of carrot (Daucus carota L.) growing in the presence of 2,4-D and by somatic embryos derived from these cultures was monitored using ¹³C nuclear magnetic resonance. The exogeneously supplied sucrose was completely hydrolyzed before cell entry; glucose was taken up preferentially when the cells were cultured in the presence of 2,4-D, while glucose and fructose were utilized at similar rates by somatic embryos in the absence of 2,4-D. Both suspension cells and somatic embryos accumulated high intracellular levels predominantly of glucose and sucrose, the latter being resynthesized intracellularly from the constitutive hexoses. Initially, fructose was converted mainly into glucose and sucrose rather than being catabolized directly through glycolysis or the pentose phosphate pathway. Carbohydrate supply that exceeded cellular demand resulted in intracellular accumulation of mono- or disaccharides. The capacity of cultured carrot cells to produce somatic embryos appeared to be positively correlated with high intracellular levels of glucose.     

HM-chromanone,a component of Portulaca oleracea L., stimulates glucose uptake and glycogen synthesis in skeletal muscle cell

BackgroundDiabetes mellitus is a chronic metabolic disease characterized by increased blood glucose levels. In order to lower blood glucose, it is important to stimulate glucose uptake and glycogen synthesis in the muscle. (E)-5-hydroxy-7-methoxy-3-(2′-hydroxybenzyl)-4-chromanone (HM-chromanone), a constituent isolated from Portulaca oleracea L., exhibits anti-diabetic effects; however, its mechanisms are not yet clearly understood on glucose uptake and glycogen synthesis in muscle cells.PurposeIn the present study, we examined the effects of HM-chromanone on glucose uptake into L6 skeletal muscle cells and elucidated the underlying mechanisms.MethodsThe effects of HM-chromanone on glucose uptake into L6 skeletal muscle cells were assessed by 2-Deoxyglucose uptake assay. Western blot analysis was carried out to elucidate the underlying molecular mechanisms.ResultsWe found that HM-chromanone promoted glucose uptake into L6 skeletal muscle cells in a dose-dependent manner. Moreover, HM-chromanone induced the phosphorylation of IRS-1^Tyr612 and AKT^Ser473, and the activation of PI3K. HM-chromanone also stimulated the phosphorylation of AMPK^Thr172, AS160^Thr642, TBC1D1^Ser237, and ACC via the CaMKKβ pathway. Furthermore, HM-chromanone increased glycogen synthesis through the inactivation of glycogen synthase kinase 3 α/β.ConclusionThe results of this study indicate that HM-chromanone stimulates glucose uptake through the activation of the PI3K/AKT and CaMKKβ-AMPK pathways and glycogen synthesis via the GSK3 α/β pathway in L6 skeletal muscle cells.     

CRITICAL POINT DRYING AS A PREPARATIVE TECHNIQUE FOR SCANNING ELECTRON MICROSCOPY AND ITS APPLICATION IN LIMNOLOGY

SUMMARY

The preservation technique of critical point drying for use with the scanning electron microscope is described. A study of the periphyton community development on the aquatic macrophyte, Potamogeton pectinatus L. from the littoral zone of Swartvlei, southern Cape Province, is used to illustrate the high degree of resolution achieved using this method.     

Post-exercise gastric emptying of carbohydrate solutions determined using the 13C acetate breath test

In an attempt to measure gastric emptying of carbohydrate solutions after exercise, we used the ¹³C acetate breath test to differentiate the gastric emptying of three approximately isoenergetic carbohydrate solutions (i.e. glucose, glucose polymer and sucrose) from each other and from water. On four separate occasions, six post-absorptive subjects walked on an inclined treadmill at 70% maximum oxygen uptake for 1 h and were then given 330 ml of one of the solutions in which 150 mg of sodium 1-[¹³C] acetate had been dissolved. Breath samples were collected at regular (2–30 min) intervals over the next 3.5 h for analysis of expired ¹³CO₂ by isotope ratio mass spectrometry. When water was given, all subjects reached peak breath enrichment after 30 min, and had a mean (SE) gastric emptying time of 33.2 (1.6) min. Peak breath enrichment occurred later for sucrose and glucose polymer at 54.3 (3.1) min and 59.0 (2.1) min respectively (P < 0.01), and for glucose this was even later, at 62.3 (1.0) min (P < 0.05). Calculated gastric emptying times for sucrose and glucose polymer were almost identical [66.5 (2.5) and 69.8 (2.9) min respectively], whereas that for glucose was significantly slower [76.8 (3.2) min; P < 0.02], probably reflecting the effects of increased osmolality. The gastric emptying of all carbohydrates were significantly longer than for water (P < 0.01). These results show that in the post-exercise state the ¹³C acetate breath test can be used to differentiate the gastric emptying rates of water and carbohydrate solutions of different properties.     

Primary metabolism of Aspergillus parasiticus in relation to aflatoxin biosynthesis

Summary The uptake of various ¹⁴C labelled compounds like (1-¹⁴C) glucose, (1-¹⁴C) acetate, (2-¹⁴C) uracil, (1-¹⁴C) leucine and (¹⁴C–CH₃) methionine was studied in Aspergillus parasiticus. A comparative study of asparagine deficient, zinc deficient and SLS cultures revealed different growth patterns. High lipid levels under zinc and asparagine deficiency were observed. During the stationary phase the synthesis of proteins and DNA declined. The uptake of ¹⁴C labelled glucose, methionine and acetate was maximum in asparagine deficient cultures during the transitional and stationary phase of growth. Maximum uptake of labelled methionine and glucose occured during the exponential growth phase (45 h). The uptake of labelled leucine was highest under asparagine deficiency during the exponential and transitional phases but reached a minimum during stationary phase. The uptake of labelled uracil remained high throughout in the asparagine deficient cultures. The mechanism of inhibition of aflatoxin biosynthesis in the absence of zinc and asparagine seems to be different.     

Effects of low water potentials on some aspects of carbohydrate metabolism in Chlorella pyrenoidosa

Summary Chlorella pyrenoidosa was subjected to low water potentials and the resulting changes in carbohydrate metabolism were measured.Water deficit reduced the incorporation of ¹⁴C-glucose into methanol insoluble compounds, principally starch and increased that into sucrose. Even moderate water deficit, for example potentials of -2.5 and -5 atm, greatly reduced the incorporation of ¹⁴C-glucose into uridine diphosphate glucose, while ¹⁴C levels of the hexose monophosphates changed little, indicating a direct stimulus of sucrose synthesis. This increased sucrose synthesis was one of the earliest effect of water deficit, because potentials of -2.5 and -5 atm did not reduce respiration and glucose uptake.At lower water potentials (-10 atm or less) there was reduced ¹⁴C incorporation into all sugar phosphates. This resulted from a combination of reduced ¹⁴C-glucose uptake and increased sucrose synthesis.Water potentials as low as -20 atm had little effect on acetate uptake, or on the ¹⁴C levels in the intermediates of the TCA cycle. This confirmed that low water potentials do not directly inhibit respiratory pathways in Chlorella.The results are discussed in relation to the effect of water deficit on levels of various metabolites in vascular plants, which have been reported by other workers.     

Fructosan metabolism in Cichorium intybus roots

Incorporation of [¹⁴C]sucrose into difructosyl glucose (F₂G), trifructosyl glucose (F₃G) and tetrafructosyl glucose (F₄G) in the presence of various nucleoside triphosphates revealed that formation of F₄G and F₃G is retarded in the presence of ATP, and formation of F₃G and F₂G is significantly enhanced in the presence of CTP, whereas UTP has no effect on the synthesis of these oligosaccharides. Different fructosyl transferases seem to be responsible for the different fructosylation steps and self transfer seems to be the major pathway for fructosan synthesis. Utilization of added glucose, which is formed by sucrose sucrose fructosyl transferase action in vivo, is completely inhibited in acetate buffer whereas in phosphate, citrate and citrate-phosphate buffers glucose is actively utilized. In the presence of fluoride ions both glucose utilization and its conversion to CO₂ is inhibited by ca 50%. CO₂ production from [¹⁴C]glucose is completely inhibited in acetate ions. No evidence for the incorporation of ¹⁴C from [¹⁴C]glucose into [¹⁴C]sucrose is observed. The ratio of bound fructose to bound glucose is the same in the entire length of the root indicating that there is no preferential zone for fructosan synthesis.     

Summer abundance and activities of bacteria in the freshwater lakes of Schirmacher Oasis,Antarctica

Bacterial biomass and heterotrophic potential (using ¹⁴C-labeled glucose, glutamic acid and sodium acetate) of water, ice and sediment microbial populations were studied from different lakes of the Schirmacher Oasis, Antarctica. Epifluorescence counts of total bacteria in these lakes were observed to be lower by a factor when compared to some of the ultraoligotrophic Antarctic lakes. Biovolumes of bacteria from different samples did not show significant variations, suggesting that regulatory factors were oligotrophy and low temperatures rather than microzoan grazing. Microbial uptake rates of glutamic acid were generally the fastest, followed by glucose and/or sodium acetate in the lakewater samples. The mean values of V_max cell^–1 for glutamic acid, sodium acetate and glucose were 3.81, 0.91 and 0.71 pgCh^–1. Results of this study are potentially useful in recognizing the relative abundance and activity of limnetic microbial populations in the Schirmacher Oasis during summer — the active period of microbial growth — and for comparing their activities with other ecosystems elsewhere in continental Antarctica.     

Glucose Metabolism and Kinetics of Phosphorus Removal by the Fermentative Bacterium Microlunatus phosphovorus

Phosphorus and carbon metabolism in Microlunatus phosphovorus was investigated by using a batch reactor to study the kinetics of uptake and release of extracellular compounds, in combination with ³¹P and ¹³C nuclear magnetic resonance (NMR) to characterize intracellular pools and to trace the fate of carbon substrates through the anaerobic and aerobic cycles. The organism was subjected to repetitive anaerobic and aerobic cycles to induce phosphorus release and uptake in a sequencial batch reactor; an ultrafiltration membrane module was required since cell suspensions did not sediment. M. phosphovorus fermented glucose to acetate via an Embden-Meyerhof pathway but was unable to grow under anaerobic conditions. A remarkable time shift was observed between the uptake of glucose and excretion of acetate, resulting in an intracellular accumulation of acetate. The acetate produced was oxidized in the subsequent aerobic stage. Very high phosphorus release and uptake rates were measured, 3.34 mmol g of cell⁻¹ h⁻¹ and 1.56 mmol g of cell⁻¹ h⁻¹, respectively, values only comparable with those determined in activated sludge. In the aerobic period, growth was strictly dependent on the availability of external phosphate. Natural abundance ¹³C NMR showed the presence of reserves of glutamate and trehalose in cell suspensions. Unexpectedly, [1-¹³C]glucose was not significantly channeled to the synthesis of internal reserves in the anaerobic phase, and acetate was not during the aerobic stage, although the glutamate pool became labeled via the exchange with intermediates of the tricarboxylic acid cycle at the level of glutamate dehydrogenase. The intracellular pool of glutamate increased under anaerobic conditions and decreased during the aerobic period. The contribution of M. phosphovorus for phosphorus removal in wastewater treatment plants is discussed on the basis of the metabolic features disclosed by this study.     

Metabolic effects of acetate in perfused rat liver studies on ketogenesis,glucose output,lactate uptake and lipogenesis

1. Livers from fed male rats were perfused in situ in a non-recirculating system with whole rat blood containing acetate at six concentrations, from 0.04 to 1.5 μmol/ml, to cover the physiological range encountered in the hapatic portal venous blood in vivo. 2. Below a concentration of 0.25 μmol/ml there was net production of acetate by the liver, while above it there was ner uptake with a fractional extraction of 40%. 3.No relationship was observed between blood [acetate] and hepatic ketogenesis, the ration [3-hydroxybutyrate]/[acetoacetate] or glucose output, either at low fatty acid concentration s or during oleate infusion. 4. Following the increase in serum fatty acid concentration, induced by oleate infusion, there were suquential incresase in ketogenesis and the ratio of [3-hydroxybutyrate]/[acetoacetate] while glucose output rose and lactate uptake fell significantly after in redox state. 5. There was a highly significant negative correlation between blood [acetate] and hepatic lactate uptake during oleate infusion. At the highest acetate concentration of 1.5 μmol/ml there was a small net hepatic lactate output. After oleate infusion ceased, lactate uptake increased, but the negative correlation between blood [acetate] and hepatic lactate uptake persisted. 6. Livers were also perfused with iether [1-¹⁴C]acetate or [U-¹⁴C]lactate at a concentration of acetate of either 0.3 or 1.3 μmol/ml of blood. With [1-¹⁴C]acetate, most of the radioactivity was recovered as fatty acids at the lower concentration of blood acetate. At the higher blood [acetate] a considerably smaller proportion of the radioactivity was recovered in lipids. With [U-¹⁴C]lactate the reverse pattern obtained i.e., recovery was greater at the high concentration of acetate and fell at the low concentration. Fatty acid biosynthesis, measured with ³H₂O, was stimulated from 2.4 to 6.6 μmol of fatty acid/g of liver per h by high blood [acetate] although the contribution of (acetate+lactate) to synthesis remained constant at 33–38% of the total. 7. These results emphasize the important role of the liver in regulating blood acetate concentrations and indicate that it can be major hepatic substrate. Acetate taken up by the liver appeared to compete directly with lactate, for lipogenesis and metabolism and acetate uptake was inhibited by raised bloodd [lactate].     

The metabolic properties of spermatozoa from the epididymis of the tammar wallaby,Macropus eugenii

The utilization of various substrates by sperm from the cauda epididymidis of the tammar was examined because the major naturally occurring sugar in the semen of this species is N-acetyl-D-glucosamine (NAG) and not fructose, as in eutherian mammals. The sperm displayed a high level of endogenous respiration that supported motility for relatively prolonged periods of time in vitro. They also metabolised exogenous ¹⁴C-labelled glucose, NAG, sucrose, and acetate through glycolytic and/or oxidative processes to produce lactate and ¹⁴CO₂ at varying rates. The rate of uptake of NAG by tammar sperm was about four times greater than that of other substrates. Glucose and/or NAG stimulated the rate of oxygen consumption by about 20%, but acetate stimulated oxygen consumption by more than 40%. The most striking findings were that NAG almost completely inhibited the oxidation of glucose and sucrose by the sperm and depressed the uptake of glucose, 3-O-methylglucose, and sucrose. Acetate oxidation also was inhibited by NAG, but only by about 50%. Tammar sperm generated substantial amounts of free glucose during incubation with NAG, but this and the inhibitory effects of NAG on glucose oxidation were not mimicked by rat sperm. It is proposed that tammar sperm fail to oxidise glucose in the presence of NAG because of the rapid cellular uptake of NAG relative to glucose. Also, the intracellular glucose and acetate liberated from NAG would compete with exogenous glucose for processing in the Embden-Meyerhof and tricarboxylic acid (TCA) cycle pathways. It is also suggested that tammar sperm oxidise sucrose after extracellular hydrolysis into its glucose and fructose components. The biological implications of these metabolic and transport properties of tammar sperm have as yet to be determined. Mol. Reprod. Dev. 49:92–99, 1998. © 1998 Wiley-Liss, Inc.