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Biomedical subjects

M Rodriguez

Publications and source records attributed to M Rodriguez.

At least 703 records · Page 39Linked to original sources
PubMed1978

Periplasmic localization of nicotinate phosphoribosyltransferase in Escherichia coli.

Nicotinate phosphoribosyltransferase (NAPRTase) in Escherichia coli mediates the formation of nicotinate mononucleotide, a direct precursor of nicotinamide adenine dinucleotide (NAD), from nicotinate and 5-phosphoribosyl-1-pyrophosphate. Specifically, NAPRTase contributes to NAD synthesis by utilizing intracellular nicotinate formed from NAD degradation products, which are recycled by NAD cycle enzymes and exogenous nicotinate when it is available. In previous studies, it has been tacitly assumed that almost all NAD cycle enzymes are localized in the cytoplasm of E. coli. The results of this investigation provide evidence that NAPRTase is a periplasmic (extracytoplasmic) enzyme. The osmotic shock of exponential-phase cells of E. coli K-12 and ML 308-225 resulted in the release of 63 to 72% and 42 to 48%, respectively, of the NAPRTase into the shock medium. In addition, when exponential cells of strains K-12 and ML 308-225 were converted into spheroplasts, 75 to 84% and 54 to 68%, respectively, of the enzyme was released into the spheroplast medium. Since previous estimates of the effective levels of NAPRTase present in putative repressed and derepressed E. coli cells appeared to be very low, a more convenient and accurate alternative method for the evaluation of NAPRTase in whole cells was developed. The results show that NAPRTase is subject only to a modest degree of enzyme repression. In addition, no evidence was found for the presence of a protein or low-molecular-weight inhibitor of the enzyme in repressed cells.

Cytoplasm↗
PubMed1978

Intramembrane changes occurring during maturation of herpes simplex virus type 1: freeze-fracture study.

During the maturation of two strains of herpes simplex virus type 1 (VR3 and Patton), intramembrane changes were detected with the freeze-fracture technique in the viral envelope and the infected cell plasma membrane, and these changes were compared with data obtained from thin sections. Regardless of the strain, the inner leaflet of the viral envelope of extracellular virions was characterized by a density of intramembrane particles (IMP) three times larger than the host nuclear and plasma membrane. Addition of IMP, which probably represent virus-coded proteins, was detected in the viral envelope only after budding from the nuclear membrane, whereas it occurred during envelopment of capsids at cytoplasmic vacuoles. Fused membranes also showed one of their fracture faces covered with a high density of IMP similar to that of the mature virion envelope. The internal side of the membrane leaflet bearing these numerous particles was always characterized by the presence of an electron-dense material in thin sections. In addition, the plasma membrane of fibroblasts and Vero cells showed strain-specific changes: patches of closely packed IMP were observed with the VR3 strain, whereas ridges almost devoid of IMP characterized the plasmalemma of cells infected with the Patton strain. These intramembrane changes, however, were not observed as early as herpes membrane antigens. Thus, application of the freeze-fracture technique to herpes simplex virus type 1-infected cells revealed striking structural differences between viral and uninfected cell membranes. These differences are probably related to insertion and clustering of virus-coded proteins in the hydrophobic part of the membrane bilayer.

Capsid↗
PubMed1977

[Peru--1977].

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Delivery of Health Care↗
PubMed1977

Junín virus infection of guinea pigs: electron microscopic studies of peripheral blood and bone marrow.

Thin sections of peripheral white blood cells and samples of bone marrow from guinea pigs infected with Junín virus were examined by electron microscopy. In peripheral blood cells, 40% of the granulocytes showed cytoplasmic lysis seven days after viral infection. After day 11 up to 80% of these cells showed morphological alterations. However, no intra- or extracellular viral particles were detected in these samples. Microscopy of bone marrow preparations revealed that 10% of the cells were altered five days after infection, and approximately 50% were affected after nine days. At this stage the megakaryocyte channels were seen to contain pleomorphic particles with a mean diameter of 80-100 nm. These particles had a unit membrane envelope and internal dense granules similar to those observed during other arenavirus infections. Therefore, it is suggested that the effect of Junín virus upon megakaryocytes may be a factor responsible for the acute thrombocytopenia observed in Argentine hemorrhagic fever.

Animals↗
PubMed1977

Neurotransmitters in spinal cord injury.

The authors report the distribution of acetylcholinesterase activity and catecholamine fluorescence in the intact and completely transected rat spinal cord. The catecholamine terminals were scarce in the posterior horn and abundant in the intermediale and anterior horn regions. In the thoracic region, intense amine fluorescence was seen in the intermediolateral cell column. Spinal transection resulted in the enhancement of fluorescence above the lesion and disappearance below the lesion within seven days. The cholinesterase activity in the controls was found mostly in the anterior horn region and the tip of the posterior horn. Following transection, there was no significant change in the distribution of this enzyme. These changes correlated with the appearance of spasticity.

Acetylcholinesterase↗