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PubMed1999

[Vitamin B1].

Vitamin B1 (thiamin), taken-up into cells, is converted to thiamin diphosphate (TDP), and TDP acts as a cofactor for several enzymes involving in carbohydrate metabolism. CoA-dependent oxidative decarboxylation of pyruvate is catalyzed by pyruvate dehydrogenase multienzyme complex (PDC) with NAD+ as an electron acceptor in most organisms involving mammals and higher plants. PDC consists of three component enzymes, one of which is pyruvate dehydrogenase (lipoamide) which contains TDP as a prosthetic group. Similar multienzyme complex for 2-oxoglutarate or branched chain 2-oxoacids is also found in mammals. In anaerobic bacteria, archaebacteria and anaerobic protozoa, pyruvate:ferredoxin oxidoreductase (PFOR) functions for the oxidative decarboxylation of pyruvate with ferredoxin in place of NAD+. PFOR contains TDP as a cofactor; however its structure is quite different from PDC and 1-3[4Fe-4S] clusters are involved as redox centers. Pyruvate:NADP+ oxidoreductase (PNOR), which catalyzes the oxidative decarboxylation of pyruvate with NADP+ as an electron acceptor, occurs in mitochondria of Euglena gracilis, a protist containing chloroplasts. PNOR consists of two functional domains, one of which contains TDP and 3[4Fe-4S] clusters and resembles PFOR. Another domain involves FMN and FAD as redox centers and its structure is similar to NADPH-cytochrom P450 reductase.

Carboxy-Lyases↗
PubMed2000

Clostridial iron-sulphur proteins.

Iron-sulfur proteins are ubiquitous catalysts of a wide range of biological reactions, and are particularly abundant in clostridia which lack the ability to synthesize hemes. The development of research on these metalloproteins has therefore been strongly associated with biochemical investigations of clostridial metabolism. Major breakthroughs in the field, from the first isolation of an iron-sulfur protein in 1962, to the recent determination of an Fe-hydrogenase structure, have been made with clostridia. These data, as well as others obtained through studies on clostridia, are transferable to many other bioenergetic machineries, due to the strong phylogenetic conservation of some important components. For instance, clear homologies exist between constituents of the anaerobic electron transfer chains in clostridia and aerobic respiratory chains. The contribution of iron-sulfur proteins to the biotechnological and medical significance of clostridia is also discussed. Structural and functional genomics are expected to bring forth a wealth of novel data on clostridia and iron-sulfur proteins.

Bacterial Proteins↗
PubMed1990

A reverse KREBS cycle in photosynthesis: consensus at last.

The Krebs cycle (citric acid or tricarboxylic acid cycle), the final common pathway in aerobic metabolism for the oxidation of carbohydrates, fatty acids and amino acids, is known to be irreversible. It liberates CO2 and generates NADH whose aerobic oxidation yields ATP but it does not operate in reverse as a biosynthetic pathway for CO2 assimilation. In 1966, our laboratory described a cyclic pathway for CO2 assimilation (Evans, Buchanan and Arnon 1966) that was unusual in two respects: (i) it provided the first instance of an obligate photoautotroph that assimilated CO2 by a pathway different from Calvin's reductive pentose phosphate cycle (Calvin 1962) and (ii) in its overall effect the new cycle was a reversal of the Krebs cycle. Named the 'reductive carboxylic acid cycle' (sometimes also called the reductive tricarboxylic acid cycle) the new cycle appeared to be the sole CO2 assimilation pathway in Chlorobium thiosulfatophilum (Evans et al. 1966) (now known as Chlorobium limicola forma thiosulfatophilum). Chlorobium is a photosynthetic green sulfur bacterium that grows anaerobically in an inorganic medium with sulfide and thiosulfate as electron donors and CO2 as an obligatory carbon source. In the ensuing years, the new cycle was viewed with skepticism. Not only was it in conflict with the prevailing doctrine that the 'one important property ... shared by all (our emphasis) autotrophic species is the assimilation of CO2 via the Calvin cycle' (McFadden 1973) but also some of its experimental underpinnings were challenged. It is only now that in the words of one of its early skeptics (Tabita 1988) 'a long and tortuous controversy' has ended with general acceptance of the reductive carboxylic acid cycle as a photosynthetic CO2 assimilation pathway distinct from the pentose cycle. (Henceforth, to minimize repetitiveness, the reductive pentose phosphate cycle will often be referred to as the pentose cycle and the reductive carboxylic acid cycle as the carboxylic acid cycle.) Aside from photosynthetic pathways which are the focus of this article, CO2 assimilation is also known to sustain autotrophic growth via the acetyl-CoA pathway (Wood et al. 1986). Our aim here is to discuss (i) the findings that led our group to the discovery of the reductive carboxylic acid cycle, (ii) the nature and resolution of the controversy that followed, and (iii) the possible evolutionary implications of the cycle as an ancient mechanism for photosynthetic CO2 assimilation that preceded the pentose cycle and served as a precursor of the Krebs cycle in aerobic metabolism.

Biological Evolution↗
PubMed2005

[Resistance of Russian isolates of Neisseria gonorrhoeae to fluoroquinolones].

Fluoroquinolones still belong to the drugs of choice in the treatment of uncomplicated gonorrhea. At the same time, there have been more data on the spreading N. gonorrhoeae strains resistant to fluoroquinolones. A variety of mechanisms, like modification of the target of antibiotic's action (point mutations in genes gyrA and parC), a decreasing permeability of the bacterial cell membrane (amino-acid changes Por protein) and a growing efflux of antibiotic (mutations in the promoter or in the coding region of mtrR) mediate in the shaping resistance of the drugs. The MIC values for four fluoroquinolone-series antibiotics were determined and the gyrA, parC, por and mtrR genes were examined for resistance-responsible mutations in 32 studied clinical strains of N. gonorrhoeae. Strains with high resistance to fluoroquinolones were detected; 3 of them had no common changes in GyrA or ParC, however, amino acid changes and mutations were detected in Por protein and promoter or gene mtrR encoding region, respectively. The paper contains priority data on the detection (in Russia) of N. gonorrhoeae strains with high resistance to fluoroquinolones. Involvement of different mechanisms in the process of resistance shaping is discussed. The results are of practical importance for planning the antibacterial therapy of gonorrhoeae; they point out the need in regional testing of resistance in the N. gonorrhoeae population encountered in Russia.

Anti-Bacterial Agents↗
PubMed2003

[Co-expressions of phosphoenolpyruvate synthetase A (ppsA) and transketolase A (tktA) genes of Escherichia coli].

Metabolic engineering is the analysis of metabolic pathway and designing rational genetic modification to optimize cellular properties by using principle of molecular biology. Aromatic metabolites such as tryptophan, phenylalanine, and tyrosine are essential amino acids for human and animals. In addition, phenylalanine is used in aspartame production. Escherichia coli and many other microoganism synthesize aromatic amino acids through the condensation reaction between phospho-enolpyruvate (PEP) and erythrose-4-phosphate(E4P) to form 3-deoxy-D-arabinoheptulosonate 7-phosphate(DAHP). But many enzymes compete for intracellular PEP, especially the phosphotransferase system which is responsible for glucose transport in E. coli. This system uses PEP as a phosphate donor and converts it to pyruvate, which is less likely to recycle back to PEP. To channel more carbon flux into the aromatic pathway, one has to overcome pathways competing for PEP. ppsA and tktA are the key genes in central metabolism of aromatic amino acids biosynthesis. ppsA encoding phosphoenolpyrucate synthetase A (PpsA) which catalyzes pyruvate into PEP; tktA encoding transketolase A which plays a major role in erythrose-4-phosphate (E4P) production of pentose pathway. We amplified ppsA and tktA from E. coli K-12 by PCR and constructed recombinant plasmids of them in pBV220 vector containing P(R)P(L) promoter. Because of each gene carrying P(L) promoter, four productions of ligation were obtained. The monoclonal host containing recombinant plasmids was routinely grown in Luria-Bertani (LB) medium added Ampicillin at 37 degrees C overnight, and then inoculated in LB (Apr) medium by 3%-5% in flasks on a rotary shaker at 30 degres C, induced at 42 degrees C for 4.5 hours when OD600 = 0.4, cells were obtained by centrifugation at 10,000 r/min at 4 degrees C. The results of SDS-PAGE demonstrated that the bands at 84kD and 73kD were more intensive than the same ones of the controls. The specific activity of PpsA in crude extracts was increased by 10.8-fold, and TktA, by 3.9-fold. When both genes were co-expressed in E. coli, the activity of PpsA varied from 2.1-9.1 fold comparing to control, but the activity of TktA was relatively stable(3.9-4.5 fold). Whatever the two genes were expressed respectively or cooperatively, both could promote the production of DAHP, the first intermediate of the common aromatic pathway, but co-expression was more effective on forming DAHP. The results demonstrate that co-expression of ppsA and tktA can improve the production of DAHP to near theoretical yield. This report details a different strategy based on co-expression of two genes in one vector in vivo to release the burden and paves the way for construction of genetic engineering bacteria for further research.

Electrophoresis, Polyacrylamide Gel↗
PubMed1987

Clostridial pyruvate oxidoreductase and the pyruvate-oxidizing enzyme specific to nitrogen fixation in Klebsiella pneumoniae are similar enzymes.

The chemical characterization, EPR properties, and mechanism of pyruvate:flavodoxin (ferredoxin) oxidoreductase from Klebsiella pneumoniae and Clostridium thermoaceticum have been investigated. A simple, specific, and sensitive assay and an efficient purification (based on the high affinity of these enzymes for a dye attached to agarose) are reported. The observed iron content of 8 atoms/subunit is twice that reported by others, whereas the contents of lipoate and flavin are less than 0.1 mol/subunit, in agreement with previous reports. Spectroscopic evidence suggests that the iron is present in Fe4S4(2+,1+) clusters. Reduction of the enzyme requires the presence of CoA as well as 1.1 pyruvate/subunit, which is very nearly the theoretical amount required the reduce two Fe4S(2+,1+) clusters. In the absence of CoA, stoichiometric amounts of pyruvate are decarboxylated, but the Fe/S centers are not reduced. We conclude that the K. pneumoniae and C. thermoaceticum enzymes are adapted to rapid reduction of low potential 1-e- carriers, similar to the pyruvate oxidoreductase of Halobacterium (Kerscher, L., and Oesterhelt, D. (1977) FEBS Lett. 83, 197-201), but different in that an Fe/S center-radical pair is used in the latter enzyme in place of the pair of Fe4S4 centers we find. The K. pneumoniae and C. thermoaceticum oxidoreductases appear to be mechanistically closely related to the Clostridium acidiurici enzyme (Uyeda, K., and Rabinowitz, J. C. (1971) J. Biol. Chem. 246, 3111-3119), differing as a class from the lipoate-containing, pyridine nucleotide-reducing enzyme present in aerobes (Reed, L. J. (1974) Accts. Chem. Res. 2, 740-746). The function of the Klebsiella enzyme is to supply electrons to nitrogenase. This is accomplished in vitro with purified components via a nif-specific flavodoxin or other low potential 1-e- carriers such as viologen dyes or ferredoxins. The in vivo molar ratio of nitrogenase to the physiological reduction system, estimated from activity measurements of individual components in crude extracts, was 0.4:0.03:2:1 pyruvate oxidoreductase:flavodoxin:nitrogenase component II:nitrogenase component I.

Acetylene↗
PubMed1987

Free radical intermediates in the reaction of pyruvate:ferredoxin oxidoreductase in Tritrichomonas foetus hydrogenosomes.

Aerobic incubations of the Tritrichomonas foetus hydrogenosomal fraction containing pyruvate, CoA, and the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) gave spectra of two radical adducts. One was a carbon-centered radical adduct of DMPO. This radical was centered at C-3 of pyruvate as determined in experiments using [13C]pyruvate. The other radical detected was identified as the CoA radical adduct of DMPO by comparison with an adduct obtained by incubating CoA with DMPO, H2O2 and horseradish peroxidase. Deletion of CoA led to an increased stability of the carbon-centered radical adduct of DMPO, disappearance of the thiyl radical adduct of DMPO, and appearance of a hydroxyl radical adduct of DMPO. Superoxide dismutase suppressed the appearance of the DMPO-hydroxyl radical adduct but did not have any inhibitory effect on the appearance of the other adducts. Catalase had no significant effect on any of the adducts. Addition of pyruvate to these hydrogenosomal preparations stimulated oxygen consumption. Addition of CoA led to a further increase in the rate of O2 uptake but had no effect in the absence of pyruvate. The formation of two substrate free radicals as intermediates in the generation of acetyl-CoA represents a novel mechanism for this enzymatic reaction and indicates that the pyruvate:ferredoxin oxidoreductase from T. foetus differs significantly from the pyridine nucleotide-dependent pyruvate dehydrogenase complex of other eukaryotic cells in its catalytic mechanism.

Electron Spin Resonance Spectroscopy↗
PubMed1982

Routes of flavodoxin and ferredoxin reduction in Escherichia coli. CoA-acylating pyruvate: flavodoxin and NADPH: flavodoxin oxidoreductases participating in the activation of pyruvate formate-lyase.

Flavodoxin and ferredoxin become reduced in Escherichia coli cells by oxidoreductase reactions which use pyruvate and NADPH as electron donor substrates. The two enzymes, which are minor proteins of this organism, were measured through the reduced flavodoxin-dependent activation of pyruvate formate-lyase. The NADPH-dependent enzyme, obtained homogeneously through Procion-red affinity chromatography, was identified as the flavoprotein 'component R' described previously by Fujii and Huennekens [J. Biol. Chem. 249, 6745-6753 (1974)]. The pyruvate-dependent enzyme was identified as CoA-acetylating pyruvate:flavodoxin (ferredoxin) oxidoreductase. Its catalytic properties in the forward, reverse, and the 14CO2-pyruvate exchange reaction are reported. The dihydro form of flavodoxin was characterized as the particular species involved in the activation of pyruvate formate-lyase. The activation process still occurs with 70% of maximal efficiency when the ratio [NADPH]/([NADP] + [NADPH]) is fixed at the intracellular 'anabolic reduction charge' value of 0.45, in conjunction with the NADPH-dependent enzyme. The [2Fe-2S] ferredoxin, though being readily used as electron acceptor of both oxidoreductases and having a redox potential similar to flavodoxin, proved incompetent in mediating the activation of pyruvate formate-lyase.

Acetyl Coenzyme A↗
PubMed1995

Primary structure and eubacterial relationships of the pyruvate:ferredoxin oxidoreductase of the amitochondriate eukaryote Trichomonas vaginalis.

In the eukaryotic unicellular organism Trichomonas vaginalis a key step of energy metabolism, the oxidative decarboxylation of pyruvate with the formation of acetyl-CoA, is catalyzed by the iron-sulfur protein pyruvate:ferredoxin oxidoreductase (PFO) and not by the almost-ubiquitous pyruvate dehydrogenase multienzyme complex. This enzyme is localized in the hydrogenosome, an organelle bounded by a double membrane. PFO and its closely related homolog, pyruvate:flavodoxin oxidoreductase, are enzymes found in a number of archaebacteria and eubacteria. The presence of these enzymes in eukaryotes is restricted, however, to a few amitochondriate groups. To gain more insight into the evolutionary relationships of T. vaginalis PFO we determined the primary structure of its two genes (pfoA and pfoB). The deduced amino acid sequences showed 95% positional identity. Motifs implicated in related enzymes in liganding the Fe-S centers and thiamine pyrophosphate were well conserved. The T. vaginalis PFOs were found to be homologous to eubacterial pyruvate:flavodoxin oxidoreductases and showed about 40% amino acid identity to these enzymes over their entire length. Lack of eubacterial PFO sequences precluded a comparison. pfoA and pfoB revealed a greater distance from related enzymes of Archaebacteria. The conceptual translation of the nucleotide sequences predicted an amino-terminal pentapeptide not present in the mature protein. This processed leader sequence was similar to but shorter than leader sequences noted in other hydrogenosomal proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

Tricarboxylic acid cycle in rat brain synaptosomes. Fluxes and interactions with aspartate aminotransferase and malate/aspartate shuttle.

The flux through different segments of the tricarboxylic acid cycle was measured in rat brain synaptosomes with gas chromatography-mass spectrometry using either deuterated glutamine or [13C]aspartate. The flux between 2-oxoglutarate and oxaloacetate was estimated to be 3.14 and 4.97 nmol/min/mg protein with and without glucose, respectively. These values were 3-5-fold faster than the flux between oxaloacetate and 2-oxoglutarate (0.92 nmol/min per mg protein) measured in the presence of glucose. The pattern of intermediates labeling suggests that the overall rate-controlling reaction involves either citrate synthase or pyruvate dehydrogenase but not 2-oxoglutarate or isocitrate dehydrogenase. The enrichment in [3,3,4,4-2H4]glutamate from [2,3,3,4,4-2H5]glutamine was as rapid as in [2,3,3,4,4-2H5]glutamate, which indicates that the aspartate aminotransferase reaction is severalfold faster than the flux through the tricarboxylic acid cycle. [13C]Aspartate was rapidly converted to [13C]malate, suggesting that in intact synaptosomes aspartate entry into the mitochondrion is very slow. The finding that aspartate is taken up by mitochondria as malate, along with the observed high enrichment in [3-2H]malate (from [2,3,3,4,4-2H5]glutamine), is consistent with the substantial synaptosomal activity of the malate/aspartate shuttle.

Animals↗
PubMed1993

Identification of the nifJ gene coding for pyruvate: ferredoxin oxidoreductase in dinitrogen-fixing cyanobacteria.

A 329 bp DNA segment from both Anabaena variabilis and Anabaena PCC 7119 was amplified using the polymerase chain reaction (PCR). The sequences from the two cyanobacteria showed strong similarities to the corresponding part of the nifJ gene from Klebsiella pneumoniae and Enterobacter agglomerans. The present findings underline earlier results of enzymatic studies that heterocystous cyanobacteria possess a pyruvate:ferredoxin (flavodoxin) oxidoreductase (PFO). The nifJ gene segment could not be detected in the non-dinitrogen-fixing, unicellular cyanobacterium Anacystis nidulans which is also in accord with previous findings from enzyme assays.

Amino Acid Sequence↗
PubMed1996

[Activity of glyoxylate cycle during the culture of Rhodotorula gracilis in the presence of fatty acids and detergents].

In this work on Rhodotorula gracilis, we studied the level of the representative enzymes of foundamental metabolic ways (HK, PK, G6PDH and IDH) and those of ICL and MS key enzymes of glyoxylate cycle with different carbone sources. The glucose appears the best source of carbone for all the tested enzymes except ICL and MS which are practically absent in the cells developed with this carbone source. In presence of acetate and ethanol we have obtained the expression of the glyoxylate cycle enzymes (ICL and MS). Moreover we obtained the operativity of the glyoxylate cycle in the lipid-rich cells or cells developped on neutral detergents or anionics similar to the fatty acids.

Detergents↗
PubMed1996

Pyruvate: ferredoxin oxidoreductase from Entamoeba histolytica recognized by a monoclonal antibody.

A mouse monoclonal antibody, Eh208C2-2 MAb, raised against whole cell antigens of Entamoeba histolytica trophozoites of the pathogenic strain HM-1: IMSS and polyclonal antisera (PAb) against membrane antigens of E. histolytica trophozoites of strain HTH-56: MUTM were screened against a cDNA library of the pathogenic strain, SFL3. The monoconal antibody detected many phage plaques expressing an E. histolytica protein. The DNA sequence encoding the protein was approximately 55% identical, over 1,100bp, to Trichomonas vaginalis pyruvate: ferredoxin oxidoreductase (PFOR) and pyruvate: flavodoxin oxidoreductase from Klebsiella pneumoniae, Anabaena variabilis and Enterobacter agglomerans. Two of seven clones detected by mouse polyclonal antisera also encoded this protein. Two others encoded Entamoeba Hsp70, another encoded Entamoeba alkyl-hydroperoxide reductase and the remaining two were unidentified sequences. Entamoeba PFOR is an abundant, antigenic protein which may be a useful target for the development of protective host immune responses against invasive amebiasis.

Amino Acid Sequence↗
PubMed2000

Enzyme profiles in two wing polymorphic soapberry bug populations (Jadera haematoloma: Rhopalidae).

Wing-polymorphic insects are excellent models for asking questions about trade-offs in physiology and life-history because of the existence of multiple morphs exhibiting numerous strategies living in one environment. We measured activities of select key enzymes in oxidative metabolism (citrate synthase), glycolysis (hexokinase, pyruvate kinase) and fatty acid oxidation (ß-hydroxyacyl CoA dehydrogenase, HOAD) in flying and non-flying long-winged bugs from two populations (ancestral and derived) of the wing-polymorphic soapberry bug (Jadera haematoloma). In the ancestral population, flyers had significantly greater activities of citrate synthase, hexokinase, pyruvate kinase, and HOAD than non-flyers. In contrast, in the derived population, flyers and non-flyers showed no significant differences in the activities of any of the enzymes tested. There were no significant differences in activities of citrate synthase as a function of adult age (3-20 d) for either population. Short-winged bugs in the derived population had significantly lower citrate synthase activities than either of the two derived, long-winged morphs, however, they were analogous to the ancestral long-winged non-flyer. These results suggest an evolution of alternative flight strategies between the two populations.

Journal Article↗
PubMed1986

Pyruvate metabolism and the phosphorylation state of isocitrate dehydrogenase in Escherichia coli.

During growth of Escherichia coli on acetate, isocitrate dehydrogenase (ICDH) is partially inactivated by phosphorylation and is thus rendered rate-limiting in the Krebs cycle so that the intracellular concentration of isocitrate rises which, in turn, permits an increased flux of carbon through the anaplerotic sequence of the glyoxylate bypass. A large number of metabolites stimulate ICDH phosphatase and inhibit ICDH kinase in the wild-type (E. coli ML308) and thus regulate the utilization of isocitrate by the two competing enzymes, ICDH and isocitrate lyase. Addition of pyruvate to acetate grown cultures triggers a rapid dephosphorylation and threefold activation of ICDH, both in the wild-type (ML308) and in mutants lacking pyruvate dehydrogenase (ML308/Pdh-), PEP synthase (ML308/Pps-) or both enzymes (ML308/Pdh-Pps-). Pyruvate stimulates the growth on acetate of those strains with an active PEP synthase but inhibits the growth of those strains that lack this enzyme. When pyruvate is exhausted, ICDH is again inactivated and the growth rate reverts to that characteristic of growth on acetate. Because pyruvate stimulates dephosphorylation of ICDH in strains with differing capabilities for pyruvate metabolism, it seems likely that pyruvate itself is a sufficient signal to activate the dephosphorylation mechanism, but this does not discount the importance of other signals under other circumstances.

Acetates↗
PubMed1988

Common ancestry of Escherichia coli pyruvate oxidase and the acetohydroxy acid synthases of the branched-chain amino acid biosynthetic pathway.

A number of enzymes require flavin for their catalytic activity, although the reaction catalyzed involves no redox reaction. The best studied of these enigmatic nonredox flavoproteins are the acetohydroxy acid synthases (AHAS), which catalyze early steps in the synthesis of branched-chain amino acids in bacteria, yeasts, and plants. Previously, work from our laboratory showed strong amino acid sequence homology between these enzymes and Escherichia coli pyruvate oxidase, a classical flavoprotein dehydrogenase that catalyzes the decarboxylation of pyruvate to acetate. We have now shown this homology (i) to also be present in the DNA sequences and (ii) to represent functional homology in that pyruvate oxidase has AHAS activity and a protein consisting of the amino-terminal half of pyruvate oxidase and the carboxy-terminal half of E. coli AHAS I allows native E. coli AHAS I to function without added flavin. The hybrid protein contains tightly bound flavin, which is essential for the flavin substitution activity. These data, together with the sequence homologies and identical cofactors and substrates, led us to propose that the AHAS enzymes are descended from pyruvate oxidase (or a similar protein) and, thus, that the flavin requirement of the AHAS enzymes is a vestigial remnant, which may have been conserved to play a structural rather than a chemical function.

Acetolactate Synthase↗
PubMed2003

Metabolic and cardiovascular adjustments of juvenile green turtles to seasonal changes in temperature and photoperiod.

We measured activity levels, oxygen consumption, metabolic enzyme activity, breathing frequency, heart rate and blood chemistry variables of juvenile green turtles exposed to a laboratory simulation of subtropical winter and summer temperatures (17-26 degrees C) and photoperiod (10.25 h:13.75 h to 14 h:10 h light:dark). The activity level of turtles had a significant effect on oxygen consumption and breathing frequency but there was no significant change in activity level between the summer and winter simulations. There was a moderate 24-27% decrease in oxygen consumption during exposure to winter conditions compared with summer conditions, but this difference was not statistically significant. Likewise, there was no statistically significant difference in breathing frequency between summer and winter simulations. Exposure to winter conditions did result in a significant decrease in activity of the aerobic enzyme citrate synthase. By contrast, activities of the glycolytic enzymes pyruvate kinase and lactate dehydrogenase were significantly higher in tissue collected during exposure to winter conditions compared with summer conditions. Citrate synthase, pyruvate kinase and lactate dehydrogenase had relatively low thermal dependence over the range of assay temperatures (15-30 degrees C; Q10=1.44-1.69). Heart rate was 46-48% lower during the winter simulation compared with the summer simulation, and this difference was statistically significant. Exposure to winter conditions resulted in a significant decrease in plasma thyroxine and plasma proteins and a significant increase in plasma creatine phosphokinase and hematocrit. Overall, our results suggest that green turtles have a relatively low thermal dependence of metabolic rate over the range of temperatures commonly experienced at tropical to subtropical latitudes, a trait which allows them to maintain activity year-round.

Animals↗