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Biomedical subjects

J P Merlie

Publications and source records attributed to J P Merlie.

120 records · Page 7Linked to original sources
PubMed1975

Synthesis of acetylcholine receptor during differentiation of cultured embryonic muscle cells.

Acetylcholine receptor, a component of the specialized muscle membrane, appears during the differentiation of embryonic myogenic cells in tissue culture. Demonstration of incorporation of the radioactive precursor L-[35S]methionine into purified receptor polypeptides is presented as evidence for its synthesis de novo. The identity of the purified radioactive species is established by cosedimentation of the [35S]receptor with [3H]alpha-toxin binding activity on sucrose gradients and by crossreaction with antiserum to purified acetylcholine receptor of Electrophorus electricus.

Acetylcholine↗
PubMed1975

Rapid cessation of phospholipid synthesis in fructose-1,6-diphosphate aldolase mutants of Escherichia coli.

Escherichia coli GH352, which was originally described as a temperature-sensitive strain containing a thermolabile acyl coenzyme A:monoacylglycerol 3-phosphate acyltransferase, does not now contain a thermolabile form of this enzyme. It has a defect in fructose-1,6-diphosphate aldolase and at least one additional temperature-sensitive lesion. Both strains GH352 and NP315, a temperature-sensitive aldolase mutant, show rapid cessation of 32-P1 incorporation into nucleic acids and phospholipids at 42 C. These characteristics of strain GH352 are therefore no longer attributed to thermolabile phospholipid synthesis, but can be attributed to the fructose-1,6-diphophate aldolase lesion.

Acyltransferases↗
PubMed1973

Effect of serine hydroxamate on phospholipid synthesis in Escherichia coli.

Serine hydroxamate, which inhibits the charging of seryl-transfer ribonucleic acid, reduced the synthesis of phospholipid and nucleic acids in Escherichia coli. This effect was analogous to depriving amino acid auxotrophs of their nutritional requirement and appears to be a manifestation of the stringent response shown by rel(+) strains of E. coli. Amino acid starvation (serine or methionine) alone or serine hydroxamate treatment alone results in 60 to 80% inhibition of lipid accumulation, 90% inhibition of ribonucleic acid accumulation, and an increase in guanosine tetraphosphate (ppGpp). These three effects were reversed by addition of chloramphenicol (CM). A combination of serine starvation and serine hydroxamate treatment resulted in inhibition of lipid and RNA accumulation as well as an increase in ppGpp, but the consequences of the double block were not reversed by CM. We conclude that a strong interrelationship exists among these processes and that CM acts to relax a stringent response by mechanisms other than interference with ppGpp formation. All species of phospholipid were affected by a stringent response evoked by amino acid starvation or addition of serine hydroxamate, but in all cases the synthesis of phosphatidylethanolamine was most severely inhibited. Serine hydroxamate was not incorporated into lipid but specifically caused phosphatidylserine accumulation. Serine starvation produced a dramatic alteration of the distribution of isotope incorporated into phospholipid, which resulted from the stringent response compounded with the limitation of a substrate for phosphatidylserine synthesis.

Adenosine Triphosphate↗
PubMed1973

Regulation of phospholipid synthesis in Escherichia coli by guanosine tetraphosphate.

Phospholipid synthesis has been reported to be subject to stringent control in Escherichia coli. We present evidence that demonstrates a strict correlation between guanosine tetraphosphate accumulation and inhibition of phospholipid synthesis. In vivo experiments designed to examine the pattern of phospholipid labeling with (32)P-inorganic phosphate and (32)P-sn-glycerol-3-phosphate suggest that regulation must occur at the glycerol-3-phosphate acyltransferase step. Assay of phospholipid synthesis by cell-free extracts and semipurified preparations revealed that guanosine tetraphosphate inhibits at least two enzymes specific for the biosynthetic pathway, sn-glycerol-3-phosphate acyltransferase as well as sn-glycerol-3-phosphate phosphatidyl transferase. These findings provide a biochemical basis for the stringent control of lipid synthesis as well as regulation of steady-state levels of phospholipid in growing cells.

Acetyltransferases↗
PubMedDate not supplied

Concentration of acetylcholine receptor mRNA in synaptic regions of adult muscle fibres.

Acetylcholine receptors (AChRs) are highly concentrated in the small fraction (approximately 0.1%) of the skeletal muscle fibre surface that comprises the postsynaptic membrane of the neuromuscular junction (Fig. 1a). In adult murine muscle, for example, AChRs are packed at a density of over 15,000 per micron2 in postsynaptic membrane, whereas their density is less than 30 per micron2 in extrasynaptic membrane. Because synaptic AChRs turn over they must be replaced, and it is interesting to consider where the new AChRs that maintain synaptic aggregates are synthesized. One possibility is that AChRs are synthesized uniformly along the length of the multinucleated muscle fibre; in this case, AChRs might be redistributed to or selectively stabilized at the synapse, as probably occurs during synapse formation. Alternatively, AChRs might be preferentially synthesized near synapses, a possibility that would suggest that innervation can influence not only where AChRs are inserted or accumulate but also where they are synthesized. In support of this second possibility, we report here that AChR messenger RNA is more abundant near to than far from synapses in adult muscle fibres.

Animals↗