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Biomedical subjects

V M Pain

Publications and source records attributed to V M Pain.

At least 55 records · Page 3Linked to original sources
PubMed1984

The metabolic state of muscle in the isolated perfused rat hemicorpus in relation to rates of protein synthesis.

Measures of perfusion adequacy in perfused rat hemicorpus preparations were investigated as potential indices of tissue function during studies of muscle protein metabolism. Perfusion under normal conditions for up to 80 min resulted in rates of protein synthesis and concentrations of ATP in muscle that were similar to those in vivo, but phosphocreatine in muscle gradually decreased and muscle lactate increased. Hypoxic conditions led to lower rates of protein synthesis, lower phospho-creatine and raised lactate contents in muscle compared with normal perfusions, and ATP was slightly decreased. Hypoxic preparations also released more lactate and K+ into the medium and had higher perfusion pressures, but glucose uptake and muscle water content were not altered. In totally ischaemic muscle, concentrations of ATP and phosphocreatine were even lower than in hypoxic muscle, and that of lactate was higher. From 11 preparations perfused for 60 min under normal conditions, three were selected on the basis of lower muscle ATP content than the others. Preparations with low ATP also showed lower muscle phosphocreatine concentrations, O2 uptake and CO2 output, as well as higher perfusion pressure and muscle lactate concentrations than in the remaining preparations, but muscle water, ADP and AMP concentrations and lactate and K+ flux were no different. In perfusions extended to 3 h, deterioration of function was more apparent. There were significant correlations between rates of protein synthesis and the concentrations of ATP, phosphocreatine and lactate in two different muscles (r = 0.756-0.929), but not with any of the other indices investigated. Taken overall, these experiments showed that concentrations of ADP, AMP and water in muscle, rates of lactate and glucose metabolism, K+ output, perfusion pressure and blood gas parameters were unsuitable for distinguishing unsound from sound preparations, because they did not consistently demonstrate differences, or could not be ascribed to only muscle metabolism. It was found that ATP, phosphocreatine and lactate concentrations in muscle were the best indicators of impaired metabolic state in studies of protein synthesis. Measurements of these could be used on a routine basis for rejecting unsatisfactory preparations.

Adenine Nucleotides↗
PubMed1984

Protein synthesis in liver and skeletal muscle of mice bearing an ascites tumor.

In mice bearing an ascites tumor at an advanced stage of growth, the weight of the gastrocnemius muscle fell, whereas that of the liver increased. Fractional rates of protein synthesis were measured in vivo under conditions designed to minimize uncertainties in the determination of the specific radioactivity of the precursor amino acid pool. Protein synthesis in liver increased in the tumor-bearing mice in comparison with controls either fed ad libitum or pair-fed to the reduced food intake of the tumor-bearing group. In muscle, the rate of protein synthesis fell substantially in comparison to ad libitum-fed controls but was not significantly different from that in a group for which food intake was restricted to that of the tumor-bearing animals.

Animals↗
PubMed1983

Radioactive puromycin formation as an assay for the proportion of active ribosomes in mammalian cells: correlation with polysome profiles under different physiological conditions.

We have established optimal conditions for the in vitro formation of peptidyl-[3H] puromycin by mammalian ribosomes. The growth conditions of cultured Ehrlich ascites tumor cells were manipulated to produce changes in the polysome profiles. The correlation between polysome content and peptidyl-[3H] puromycin formation was linear and excellent when different cell densities were compared. The percentage of ribosomes actively engaged in protein synthesis, calculated from the number of 3H-peptide bonds formed, was similar in rapidly growing Ehrlich cells (47%) and in young rat gastrocnemius muscle (44%). Starvation resulted in a 50% reduction in the number of puromycin-reactive ribosomes in rat gastrocnemius.

Animals↗
PubMed1983

Assembly and breakdown of mammalian protein synthesis initiation complexes: regulation by guanine nucleotides and by phosphorylation of initiation factor eIF-2.

Eukaryotic cell polypeptide chain initiation factor eIF-2 forms ternary complexes with GTP and initiator Met-tRNAf. These complexes can be destabilized in vitro by the addition of salt-washed 40S ribosomal subunits. Our evidence suggests that this destabilization is mediated by GDP generated by premature hydrolysis of the GTP molecule present in the ternary complex. With complexes formed by using a partially purified preparation of eIF-2 from Ehrlich ascites tumor cells, it is possible to reverse the 40S subunit induced inhibition by creating conditions which eliminate free GDP from the system. This reversal probably occurs due to exchange of GTP for the GDP bound to the initiation factor, in a reaction catalyzed by another factor present in the eIF-2 preparation. However, if the eIF-2 has previously been phosphorylated by the reticulocyte heme-controlled repressor, the 40S subunit induced inhibition cannot be reversed by elimination of free GDP. The instability of initiation complexes containing eIF-2, together with the impairment of guanine nucleotide exchange after phosphorylation of eIF-2 [Clemens, M.J., Pain, V.M., Wong, S.-T., & Henshaw, E. C. (1982) Nature (London) 296, 93-95], may be an important aspect of the mechanism of the inhibition of translation by the heme-controlled repressor.

Animals↗
PubMed1983

Protein metabolism in skeletal muscle, diaphragm, and heart of diabetic rats.

Rates of protein synthesis were measured in several muscle types in young streptozotocin-diabetic rats at different times after withdrawal of insulin therapy. Protein synthesis decreased in all types of muscle studied. In muscles with a substantial proportion of fast-twitch fibers (gastrocnemius and extensor digitorum longus), this decline was associated with falls in both protein synthesis-to-RNA and RNA-to-protein ratio, but in soleus and heart the effect could be explained entirely in terms of decreased ribosome concentration. Rates of protein degradation were calculated for heart, diaphragm, and gastrocnemius muscle from the changes in protein synthesis and protein content and were found in all cases to be elevated by 4 days of insulin withdrawal. However, measurements of protein synthesis and protein mass in the gastrocnemius muscle of a group of chronically diabetic rats indicated that in this condition, unlike in acute diabetes, the rate of protein degradation was depressed.

Animals↗
PubMed1982

Regulation of binding of initiator tRNA to eukaryotic initiation factor eIF-2. Effects of the haem-controlled repressor on the kinetics of ternary complex formation.

Ternary complex formation was studied in reticulocyte lysate supernatants and using rat liver eukaryotic initiation factor-2 (eIF-2) preparations. Haem-deficiency reduced the rate of formation of ternary (Met-tRNAf . GTP . eIF-2) complexes by the eIF-2 in reticulocyte supernatants, the reduction being more marked when complex formation was assayed in the absence of GTP-regenerating capacity. Pretreatment with the haem-controlled repressor (HCR) reduced the rate of ternary complex formation by crude (liver) eIF-2. In contrast, complex formation by an almost homogeneous eIF-2 preparation was unaffected by HCR: sensitivity to HCR was however restored by a factor which catalyses exchange of guanine nucleotides bound to eIF-2.

Animals↗
PubMed1981

Association of initiation factor eIF-2 with a rapidly sedimenting fraction from Ehrlich ascites-tumour cells.

To determine the subcellular distribution of initiation-factor eIF-2 activity, Ehrlich ascites-cell homogenates were fractionated to give (a) a rapidly sedimenting fraction, (b) a microsomal fraction and (c) post-microsomal supernatant. The first two fractions were washed in 0.5 m-KCl to render the associated protein-synthesis factor soluble. As much as 60% of the total recoverable eIF-2 was obtained from the rapidly sedimenting material.

Animals↗
PubMed1981

Protein turnover in tissues of diabetic rats.

Rates of protein breakdown in tissues of diabetic rats were estimated by measuring the rates of protein synthesis and growth of protein mass. Measurements were made after withdrawal of insulin from streptozotocin diabetic rats that had been maintained with daily insulin injections. In muscle of the control (insulin treated) rats there was rapid catch up growth associated with increased protein synthesis and decreased breakdown. Insulin withdrawal resulted in a loss of protein, a decreased rate of synthesis and an elevated rate of breakdown. In the liver of the insulin withdrawn rats there was an immediate loss of protein associated with reduced synthesis and increased breakdown, but after two days the protein loss ceased and breakdown was also depressed. The response of kidney to insulin withdrawal was an increase in protein mass, brought about entirely by an inhibition of proteolysis.

Animals↗
PubMed1980

The effects of amino acid starvation on regulation of polypeptide chain initiation in Ehrlich ascites tumor cells.

The ratio of initiation of protein synthesis in Ehrlich ascites tumor cells in culture is reduced by over 60% in the absence of a single essential amino acid. Cell-free extracts prepared from control and amino acid-starved cells retain some of the translational characteristics of these cells and are able to form [40 S.Met-tRNAfMet] initiation complexes. Studies with inhibitors show that up to 63% of the translation directed by endogenous mRNAs in vitro depends on reinitiation of polypeptide chains. Amino acid starvation inhibits this activity, as well as protein synthesis due to in vitro polysomal run-off, by up to 75%. Analysis of [40 S.Met-tRNAfMet]initiation complexes formed in vitro on native 40 S subunits shows that amino acid starvation causes up to a 77% decrease in the concentration of these complexes relative to the corresponding fed controls. This difference is eliminated by the addition of highly purified eukaryotic initiation factor eIF-2. Factor eIF-3 also stimulates [40 S.Met-tRNAfMet] formation in the cell extracts but does not abolish the difference between fed and starved preparations. Mixing experiments have not so far revealed any inhibitor of initiation complex formation in the starved cell extracts.

Amino Acids↗