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The effect of a growth promoting drug, clenbuterol, on fibre frequency and area in hind limb muscles from young male rats.

The effect of dietary administration of clenbuterol on soleus and extensor digitorum longus muscles was studied after 4 and 21 days. Both muscles showed an increase in wet weight with no significant change in total fibre number. After 4 days fibre cross-sectional areas were increased in soleus, but not in extensor digitorum longus, and after 21 days there was a change in fibre frequencies in extensor digitorum longus but not soleus muscles.

Animals↗

NADH-reductive stress in Saccharomyces cerevisiae induces the expression of the minor isoform of glyceraldehyde-3-phosphate dehydrogenase (TDH1).

A strain of Saccharomyces cerevisiae lacking the GPD2 gene, encoding one of the glycerol-3-phosphate dehydrogenases, grows slowly under anaerobic conditions, due to reductive stress caused by the accumulation of cytoplasmic NADH. We used 2D-PAGE to study the effect on global protein expression of reductive stress in the anaerobically grown gpd2Delta strain. The most striking response was a strongly elevated expression of Tdh1p, the minor isoform of glyceraldehyde-3-phosphate dehydrogenase. This increased expression could be reversed by the addition of acetoin, a NADH-specific redox sink, which furthermore largely restored anaerobic growth of the gpd2Delta strain. Additional deletion of the TDH1 gene (but not of TDH2 or TDH3) improved anaerobic growth of the gpd2Delta strain. We therefore propose that TDH1 has properties not displayed by the other TDH isogenes and that its expression is regulated by reductive stress caused by an excess of cytoplasmic NADH.

Acetoin↗

Dietary TAG source and level affect performance and lipase expression in larval sea bass (Dicentrarchus labrax).

The influence of dietary TAG source (fish oil, triolein, and coconut oil) and level (7.5 and 15% of the diet) on growth, lipase activity, and mRNA level was studied in sea bass larvae, from mouth opening until day 24 and from day 37 to 52. Fish oil and triolein induced better growth in both experiments, this being significant at a higher dietary level. Coconut oil significantly decreased growth at the higher level, possibly as the result of an excessive supply of medium-chain TAG. Growth was not related to lipase specific activity, suggesting a production in excess to dietary needs. Body lipid content was positively related to dietary lipid level and was affected by lipid quality. In addition, larval FA composition generally reflected that of the diet. The source of dietary lipid, but not the quantity, was shown to affect lipase activity significantly. Coconut oil diets induced the highest lipase activity, whereas the effect of fish oil was age dependent-it was similar to coconut oil at day 24 but induced the lowest lipase activity in 52-d-old larvae. The differential lipase response was probably caused by differences in the FA composition of the diet, related to the specificity of lipase toward FA differing in chain length and degree of saturation. No significant differences were found in lipase/glyceraldehyde-3-phosphate dehydrogenase mRNA, which suggests the existence of a posttranscriptional regulation mechanism.

Age Factors↗

An enzymatic assay for picomole levels of phosphatidate.

An assay for phosphatidate that is sensitive, specific, and highly reproducible is described. Phosphatidate is transacylated with methylamine and the glycerol 3-phosphate produced is measured enzymatically. The assay is linear from 50 to 1500 pmol of phosphatidate and can be used to quantitate phosphatidate in small amounts of biological materials.

Animals↗

Osmoregulation in Saccharomyces cerevisiae. Studies on the osmotic induction of glycerol production and glycerol-3-phosphate dehydrogenase (NAD+)

Production of glycerol and a key enzyme in glycerol production, glycerol 3-phosphate dehydrogenase (NAD+) (GPD), was studied in Saccharomyces cerevisiae cultured in basal media or media of high salinity, with glucose, raffinose or ethanol as the sole carbon source. At high salinity, glycerol production was stimulated with all carbon sources and glycerol was accumulated to high intracellular concentration in cells grown on glucose and raffinose. Cells grown on ethanol accumulated glycerol to a lower level but showed an increased content of trehalose at high salinity. However, the trehalose concentration corresponded only to about 20% of the glycerol level, and did not compensate for the shortfall in intracellular osmolyte content. Immunoblot analysis demonstrated an increased production of GPD at high salinity. This increase was osmotically mediated but was lower when glycerol was substituted for NaCl or sorbitol as the stress-solute. The enzyme also appeared to be subject to glucose repression; the specific activity of GPD was significantly lower in cells grown on glucose, than on raffinose or ethanol.

Ethanol↗

Molecular characterization of glycosomal NAD(+)-dependent glycerol 3-phosphate dehydrogenase from Trypanosoma brucei rhodesiense.

The primary structure of a 38-kDa protein isolated from membrane preparations of African trypanosomes was determined by protein and DNA sequencing. Searching of the protein database with the trypanosome translated amino acid sequence identified glycerol 3-phosphate dehydrogenase (EC 1.1.1.8) from various prokaryotic and eukaryotic organisms as the optimal scoring protein. Surprisingly, the eukaryotic trypanosome enzyme showed the highest degree of sequence identity with the corresponding enzyme from the prokaryote Escherichia coli. The trypanosome molecule was expressed in Escherichia coli and found to be enzymatically active, thus confirming the identity of the molecule as an NAD(+)-dependent glycerol 3-phosphate dehydrogenase. A monoclonal antibody specific for the 38-kDa protein was used to localize the enzyme to glycosomes. Immunoblotting showed that the monoclonal antibody bound to a 38-kDa protein in African trypanosomes but not in T. cruzi, Leishmania or Crithidia. The enzyme has a pI of 9.1, a net charge of +17 and contains the peroxisome-like targeting tripeptide SKM at its C-terminus, all characteristic of glycosomal enzymes. Amino acids predicted to be involved in the NAD(+)-dependent glycerol 3-phosphate dehydrogenase active site have diverged from those of the mammalian enzyme. Kinetic analyses of the trypanosome GPD and GPD from rabbit muscle showed that the Km values of the two enzymes are different. The data suggest that the trypanosome protein may be a candidate target for rational drug design.

Amino Acid Sequence↗

Cloning and characterization of the NAD-linked glycerol-3-phosphate dehydrogenases of Trypanosoma brucei brucei and Leishmania mexicana mexicana and expression of the trypanosome enzyme in Escherichia coli.

A polyclonal antiserum raised against the purified glycosomal glycerol-3-phosphate dehydrogenase of Trypanosoma brucei brucei has been used to identify the corresponding cDNA clone in a T.b. brucei expression library. This cDNA was subsequently used to obtain genomic clones containing glycerol-3-phosphate dehydrogenase genes. Two tandemly arranged genes were detected in these clones. Characterization of one of the genes showed that it codes for a polypeptide of 353 amino acids, with a molecular mass of 37,651 Da and a calculated net charge of +8. Using the T.b. brucei gene as a probe, a corresponding glycerol-3-phosphate dehydrogenase gene was also identified in a genomic library of Leishmania mexicana mexicana. The L.m. mexicana gene codes for a polypeptide of 365 amino acids, with a molecular mass of 39,140 Da and a calculated net charge of +8. The amino-acid sequences of both polypeptides are 63% identical and carry a type-1 peroxisomal targeting signal (PTS1) SKM and -SKL at their respective C-termini. Moreover, the L.m. mexicana polypeptide also carries a short N-terminal extension reminiscent of a mitochondrial transit sequence. Subcellular localisation analysis showed that in L.m. mexicana the glycerol-3-phosphate dehydrogenase activity co-fractionated both with mitochondria and with glycosomes. This is not the case in T. brucei, where the enzyme is predominantly glycosomal. The two trypanosomatid sequences resemble their prokaryotic homologues (32-36%) more than their eukaryotic counterparts (25-31%) and carry typical prokaryotic signatures. The possible reason for this prokaryotic nature of a trypanosomatid glycerol-3-phosphate dehydrogenase is discussed.

Amino Acid Sequence↗

Molecular cloning, sequencing and expression of a cDNA encoding a human liver NAD-dependent alpha-glycerol-3-phosphate dehydrogenase.

This work reports the primary nucleotide structure and in vitro translation of a cDNA, expressed by a gene mapping on chromosome 12, that encodes a human hepatic alpha-glycerol-3-phosphate dehydrogenase (L-glycerol-3-phosphate:NAD oxidoreductase, E.C. 1.1.1.8). The 1413 bp cDNA comprises an ORF of 1050 bp that encodes a 349 amino acid protein of 37.5 kDa. Northern blot analysis of poly(A)+ mRNA from human liver showed three transcripts, while from human placenta only two transcripts were detected.

Amino Acid Sequence↗

Ortho-phenanthroline modulates enzymes of cellular energy metabolism.

The lipophilic iron chelator 1,10-phenanthroline has been used in mechanistic studies on intracellular oxidant damage because iron is assumed to play a role in the endogenous formation of highly reactive oxygen species. This study shows that 1,10-phenanthroline has enzyme-modulatory properties in addition to its antioxidant activity. In rat hepatocytes, 1,10-phenanthroline caused inhibition of respiration and enhancement of cellular ATP content, pyruvate release and CO2 formation from glycerol resulting from a modulatory action of 1,10-phenanthroline on various enzymes involved in cellular energy metabolism. In intact mitochondria and in submitochondrial particles, oxygen consumption, complex I activity, and ATPase degradation are inhibited by 1,10-phenanthroline. In submitochondrial particles, complex II activity can also be suppressed by 1,10-phenanthroline. The purified cytosolic enzymes lactate dehydrogenase and glycerol-3-phosphate dehydrogenase are inhibited while purified glyceraldehyde-3-phosphate dehydrogenase is activated by 1,10-phenanthroline. The results suggest that 1,10-phenanthroline modulates various enzyme activities linked to cellular energy metabolism and that this property must be taken into account when using 1,10-phenanthroline as a tool in experiments on oxidant effects in cells.

Adenosine Triphosphatases↗

Molecular analysis of a Drosophila melanogaster sn-glycerol-3-phosphate dehydrogenase allozyme variant that has cold labile activity.

A rare naturally occurring allele, GpdhACb62, at the sn-glycerol-3-phosphate dehydrogenase locus in Drosophila melanogaster, encodes an enzyme with an electrophoretic mobility that is more cathodal than that produced by the common slow electrophoretic allele. After electrophoresis and staining of extracts of single adult flies there is a single band of activity corresponding in position to GPDH-1, but, using highly concentrated extracts, a faint band corresponding to GPDH-3 is observed. In GpdhACb62 homozygotes there is about 26% of the normal level of activity in adults, and less than 6% in third instar larvae. The reduction in activity is significantly greater than the decrease in GPDH immunologically cross-reacting material (CRM). Northern analyses, and rapid amplification of the cDNA ends (RACE) of the 3' regions of the transcripts, show that the levels and structures of the poly(A)+RNAs are similar in homozygotes for GpdhACb62 and for a normal activity allele GpdhAC8. Hybridization to oligonucleotide probes specific for the GPDH-1 and GPDH-3 transcripts was of a similar intensity in GpdhACb62 and GpdhAC8 adult flies. In third instar larvae the main transcript is for GPDH-3 and again the hybridization signals were similar in each line. The activity of the enzyme produced by GpdhACb62 was unstable both at 50 degrees C and at 0 degrees C. The activity lost at 0 degrees C was recovered by incubation at 20 degrees C. The complete GpdhACb62 gene, and the partial Gpdh tandem duplication 3' to this gene, were cloned and sequenced. Comparisons with two normal activity GpdhF genes revealed 31 unique changes in the first copy of GpdhACb62. In exon 4, a T to G substitution changes cysteine to glycine and may disrupt a disulphide bond and be responsible for the distinctive properties of GPDH-ACb62.

Alleles↗