Effect of carbon dioxide on yeast growth and fermentation

The duration and completeness of recovery from anaerobic metabolism is of important functional consequence in invertebrates. Two basic processes occur during recovery: (1) recharging of the phosphagen and ATP pools and (2) disposal of end products by excretion, oxidation, or conversion back to anaerobic substrates. The recovery process in invertebrates is largely aerobic, as is evidenced by the near universality of the oxygen debt phenomenon. However, there is often a lack of correlation between end product accumulation and the magnitude of the oxygen debt. Typically, ATP and phosphagen levels are recharged very rapidly during recovery–ATP (0.25 to 1.0 hr) and phosphagens (0.5 to 4 hr). Excretion of propionate, acetate, and, occasionally succinate, is relatively common in annelids and has also been observed in a number of bivalve molluscs. Nitrogen-containing end products do not appear to be excreted. Cephalopods and large arthropods show elevated hemolymph end product levels following anoxia/hypoxia. In arthropods, these end products display a protracted return to control levels during recovery. In cephalopods, some octopine may be rapidly taken up and metabolized by the heart, brain, and gill. The sites of lactate metabolism in arthropods are unclear. In contrast to the situation in cephalopods and arthropods, most end products in the adductor muscles of bivalve molluscs do not appear to be exported, but are metabolized within the tissue itself. End ducts such as octopine, succinate, and alanine thus appear to be metabolized at the site of their production. Octopine and lactate appear to be gluconeogenic substrates in cephalopods and arthropods, respectively. Although many of the enzymes involved in gluconeogenesis are present in bivalve molluscs, this process has not been demonstrated in this group. Recovery from anaerobic metabolism remains a fruitful area for future research. Of special interest is the identification of sites of gluconeogenesis in the larger, more active species.

The recovery from anaerobic metabolism in invertebrates

Protists that live in low oxygen conditions often oxidize pyruvate to acetate via anaerobic ATP-generating pathways. Key enzymes that commonly occur in these pathways are pyruvate:ferredoxin oxidoreductase (PFO) and [FeFe]-hydrogenase (H(2)ase) as well as the associated [FeFe]-H(2)ase maturase proteins HydE, HydF, and HydG. Determining the origins of these proteins in eukaryotes is of key importance to understanding the origins of anaerobic energy metabolism in microbial eukaryotes. We conducted a comprehensive search for genes encoding these proteins in available whole genomes and expressed sequence tag data from diverse eukaryotes. Our analyses of the presence/absence of eukaryotic PFO, [FeFe]-H(2)ase, and H(2)ase maturase sequences across eukaryotic diversity reveal orthologs of these proteins encoded in the genomes of a variety of protists previously not known to contain them. Our phylogenetic analyses revealed: 1) extensive lateral gene transfers of both PFO and [FeFe]-H(2)ase in eubacteria, 2) decreased support for the monophyly of eukaryote PFO domains, and 3) that eukaryotic [FeFe]-H(2)ases are not monophyletic. Although there are few eukaryote [FeFe]-H(2)ase maturase orthologs characterized, phylogenies of these proteins do recover eukaryote monophyly, although a consistent eubacterial sister group for eukaryotic homologs could not be determined. An exhaustive search for these five genes in diverse genomes from two representative eubacterial groups, the Clostridiales and the alpha-proteobacteria, shows that although these enzymes are nearly universally present within the former group, they are very rare in the latter. No alpha-proteobacterial genome sequenced to date encodes all five proteins. Molecular phylogenies and the extremely restricted distribution of PFO, [FeFe]-H(2)ases, and their associated maturases within the alpha-proteobacteria do not support a mitochondrial origin for these enzymes in eukaryotes. However, the unexpected prevalence of PFO, pyruvate:NADP oxidoreductase, [FeFe]-H(2)ase, and the maturase proteins encoded in genomes of diverse eukaryotes indicates that these enzymes have an important role in the evolution of microbial eukaryote energy metabolism.

/pdf/phylogenetic-distributions-and-histories-of-proteins-24p6vtnd2a.pdf

Phylogenetic Distributions and Histories of Proteins Involved in Anaerobic Pyruvate Metabolism in Eukaryotes

Pelteobagrus vachelli is a well-known commercial species in Asia. However, a sudden lack of oxygen will result in mortality and eventually to pond turnover. Studying the molecular mechanisms of hypoxia adaptation in fishes will not only help us to understand fish speciation and the evolution of the hypoxia-signaling pathway, but will also guide us in the breeding of hypoxia-tolerant fish strains. Despite this, the genetic regulatory network for miRNA-mRNA and the signaling pathways involved in hypoxia responses in fish have remained unexamined. In the present study, we used next-generation sequencing technology to characterise mRNA-seq and miRNA-seq of control- and hypoxia-treated P. vachelli livers to elucidate the molecular mechanisms of hypoxia adaptation. We were able to find miRNA-mRNA pairs using bioinformatics analysis and miRNA prediction algorithms. Furthermore, we compared several key pathways which were identified as involved in the hypoxia response of P. vachelli. Our study is the first report on integrated analysis of mRNA-seq and miRNA-seq in fishes and offers a deeper insight into the molecular mechanisms of hypoxia adaptation. qRT-PCR analysis further confirmed the results of mRNA-Seq and miRNA-Seq analysis. We provide a good case study for analyzing mRNA/miRNA expression and profiling a non-model fish species using next-generation sequencing technology.

Integrated analysis of mRNA-seq and miRNA-seq in the liver of Pelteobagrus vachelli in response to hypoxia

With few exceptions, the specific activities of the glycolytic enzymes and the steady-state content of glycolytic and associated intermediates in protoscoleces of the horse (E.g.H) and sheep (E.g.S) strains of Echinococcus granulosus and the closely related E. multilocularis (E.m.) are very similar. Phosphorylase, hexokinase, phosphofructokinase and pyruvate kinase catalyse non-equilibrium reactions and the patterns of activity for pyruvate kinase, phosphoenolpyruvate carboxykinase and malic enzyme are similar in the three organisms. The levels of tricarboxylic acid cycle intermediates in E.g.H., E.g.S. and E.m. are of the same order as those reported in tissues with an active cycle. Each has a complete sequence of cycle enzymes but there are substantial differences between the three parasites with regard to the activity of individual enzymes, The activities of NAD and NADP-linked isocitrate dehydrogenases are significantly lower in E.g.H. than in E.g.S. and particularly in E.m. which suggests that the tricarboxylic acid cycle may play a more important role in carbohydrate metabolism and energy production in the latter parasites. Nevertheless, the three organisms utilize fermentative pathways for alternative energy production, fix carbon dioxide via phosphoenolpyruvate carboxykinase and have a partial reversed tricarboxylic acid cycle. It is speculated that in vivo more carbon will be channelled towards oxaloacetate than pyruvate at the phosphoenolpyruvate branch point. The steady state content of ATP and the ATP/AMP ratios are low in the three organisms, suggesting a low rate of ATP utilization in each.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0031182000044899

Intermediary carbohydrate metabolism in protoscoleces of Echinococcus granulosus (horse and sheep strains) and E. multilocularis.

1.

During anaerobic exposure ofTubifex, lactate and alanine increase only within the first 24 h, while concentrations of succinate, propionate and also acetate continually increase under prevailing anaerobic conditions. Enzymes involved in anaerobic energy metabolism were isolated, and the effects of various metabolites and inorganic compounds on their catalytic properties studied.




2.

The specific activities of the cytosolic enzymes LDH, PK, MDH, and PEPCK, and of mitochondrial malic enzyme and MDH are high.




3.

Under conditions of high HCO3− (HCO3−+CO2 system), PEPCK is maximally active while PK is inhibited.




4.

The catalytic properties of mitochondrial malic enzyme indicate that in vivo this enzyme operates in the direction of malate decarboxylation.




5.

The cytosolic oxidoreductases LDH and MDH were examined with regard to the maintenance of redox state. Function of MDH is only subject to substrate availability, while the enzyme-substrate affinity of LDH might be affected by pH to a limited extent.




6.

The data support the conclusion that total CO2, fructose-1,6-diphosphate concentration, the adenylate energy charge, and-only to a limited extent-the intracellular pH are regulatory signals which govern PEP metabolism inTubifex.

Role of pyruvate kinase, phosphoenolpyruvate carboxykinase, malic enzyme and lactate dehydrogenase in anaerobic energy metabolism ofTubifex spec

1.

Phosphoenolpyruvate carboxykinase from four facultative anaerobic invertebrate species is shown to decarboxylate oxalacetate to phosphoenolpyruvate (Table 1). Knowledge of this reaction is of importance in the evaluation of gluconeogenic capacities of these organisms.




2.

InTubifex the PEPCK-catalyzed decarboxylation reaction was characterized and its regulatory properties were studied. PEPCK mainly occurs in the cytosolic fraction and its absolute requirements in the decarboxylation direction are oxalacetate, Mn2+, nucleoside triphosphate (ITP) (Table 2). The pH optima for PEPCK-catalyzed decarboxylation and carboxylation reactions are 8.1 and 7.1, respectively (Fig. 1).Km values for oxalacetate and ITP were 0.25 and 0.39 mM, respectively (Fig. 2b and c). In presence of 0.5 mM AMP, the decarboxylation reaction was inhibited up to 50% of the control while even in presence of 5 mM AMP, the carboxylation reaction was unaffected (Fig. 3). Lombricine phosphate, one of the naturally occurring phosphagens inTubifex, activates the PEPCK-catalyzed decarboxylation reaction. 3-Mercaptopicolinic acid, a known specific inhibitor of vertebrate and invertebrate PEPCKs, also inhibitsTubifex PEPCK (Table 3).




3.

UnlikeCrassostrea andAscaris, pyruvate carboxylase activity is present inTubifex tissues which will facilitate the conversion of C3 to C4 compounds and thus their eventual incorporation into glycogen.




4.

Various gluconeogenic precursors when provided exogenously under aerobic conditions are incorporated into tissue glycogen by the intactTubifex (Table 4).




5.

The potential roles of PEPCK regulatory properties under aerobic and anaerobic conditions are discussed with relation to gluconeogenesis and glycolysis inTubifex.

Gluconeogenesis in facultative anaerobic invertebrates: Evidence of oxalacetate decarboxylation and anaerobic end product incorporation into glycogen from the tissues ofTubifex sp.

T. Mustafa

Papers

Role of pyruvate kinase, phosphoenolpyruvate carboxykinase, malic enzyme and lactate dehydrogenase in anaerobic energy metabolism ofTubifex spec

Gluconeogenesis in facultative anaerobic invertebrates: Evidence of oxalacetate decarboxylation and anaerobic end product incorporation into glycogen from the tissues ofTubifex sp.