PubMed Health⌕ Search

Biomedical subjects

L M Popa

Publications and source records attributed to L M Popa.

At least 19 recordsLinked to original sources
PubMed1996

Specific targeting of human papillomavirus type 16 E7 oncogene with triple-helix forming purine oligodeoxyribonucleotides.

Molecular mechanical calculations (computer modelling), optical DNA melting experiments and co-migration assay were used to assess stable helix formation at homopurine-homopyrimidine-rich target sites present in the human papillomavirus type 16 E7 oncogene (positions 656-673 on the genome map). The target sequence, either present in the E7 oncogene obtained by PCR technique or prepared from oligodeoxyribonucleotides (ODNs), can be specifically recognised by different 17-merpurine ODNs designed to form antiparallel or parallel triple helices. These "in vitro" experiments realised with rather long purine ODNs having a high degree of specificity, open the way for "in vivo" tests focused on E7 oncogene targeting and suppression.

Base Sequence↗
PubMed1994

Some new properties of DNA-YOYO-3 homodimer complexes revealed by electrophoresis and fluorescence lifetime measurements.

The DNA bis-intercalator oxazole homodimer (YOYO-3: 1,1'-(4,4,7,7-tetramethyl-4,7-diazaundecamethylene)-bis-4-[3-methy l- 2,3-dihydro-(benzo-1,3-oxazole)-2-methylidene]-quinolinium tetraiodide) specifically alters the electrophoretic pattern of covalently closed circular (CCC) DNA molecules. Thus, YOYO-3 seems to remove the CCC DNA supercoils and induces the appearance of additional bands by changing the linking number. It also promotes an unusual "star" activity for the restriction enzyme Hind III. Fluorescence lifetime measurements indicate that YOYO-3 is capable of binding to DNA by bis- and mono-intercalation.

Benzoxazoles↗
PubMed1985

Some physico-chemical and biological properties of egg-Sendai virus with altered haemagglutinin-neuraminidase protein.

Some physico-chemical and biological properties of egg-cultivated Sendai (egg-Sendai) virus particles with altered haemagglutinin-neuraminidase (HN) protein were studied. These particles were obtained accidentally from purified egg-Sendai virus stored at +4 degrees C. Egg-Sendai with altered HN protein was not infectious for cultured cells, but could still infect embryonated eggs. Though egg-Sendai virus with altered HN protein and glycoproteins had no haemagglutination activity, it unexpectedly possessed a relatively high neuraminidase (NA) activity representing about 70% of the activity of normal particles. Since polyacrylamide gel and rocket immunoelectrophoresis indicated that the altered particles contained only F protein, possibly the native HN was converted into a molecule of the same molecular mass as F protein.

Antigens, Viral↗
PubMed1985

Effect of some anthracycline antibiotics on the neuraminidase activity of Sendai virus and its isolated glycoproteins.

Anthracycline antibiotics violamycin BI (VBI) and adriamycin (Adr) strongly inhibited the neuraminidase (NA) activity of Sendai virus and of its isolated glycoproteins, occurring either in solution or associated in liposome-like particles. NA did not exhibit the classical Michaelis-Menten kinetics: the plot of reaction velocity versus substrate concentration was sigmoidal, while Hill's plotting indicated that the enzyme has at least two binding sites for the substrate. The reaction kinetics obtained suggested that Sendai virus NA acts as an allosteric enzyme, when its material support, the HN is located on the virus surface. The inhibitory effect of the anthracycline antibiotics in question on the NA activity seemed to be similar to that of negative effectors.

Allosteric Site↗
PubMed1979

Specific alteration of Sendai virus glycoprotein subunits.

The alteration produced by chemical and physical agents in the structure and neuraminidase activity of Sendai virus glycoproteins was studied. While dissociation of glycoproteins with 1% sodium dodecyl sulphate (SDS), 2% beta-mercaptoethanol and 5 M urea for 2 min at 100 degrees C yielded the known HN and F subunits (mol. wts. 60,000 and 53,000), in the presence of 1% SDS the glycoproteins were converted into components with approximate mol. wts. of 60,000, 120, 000 and higher. Treatment of the glycoproteins with 2% beta-mercaptoethanol and 0.1% SDS favoured the formation of a single component with a mol. wt. of 75,000. The alterations in the glycoprotein structure were very likely caused by their free -SH groups content. An average value of 6 free -SH groups per glycoprotein subunit was estimated. Glycoproteins stored at 4 degrees C contained only 53,000 mol. wt. subunits. During storage a kind of conversion of 67,000 to 53,000 mol. wt. components took place, preserving about 60% of the initial neuraminidase activity.

Glycoproteins↗
PubMed1978

Influence of the isolation procedure on the structure, neuraminidase and heamagglutinating activities of Sendai virus envelope glycoproteins.

The influence of the isolation procedure of Sendai virus glycoproteins from the virus surface on their neuraminidase and haemagglutinating activities, as well as on some structural properties was studied. These glycoproteins exhibited lower specific neuraminidase and haemagglutinating activities than those of intact virus. Neuraminidase activity was expressed when the glycoproteins were constituted in forms with molecular weights of about 70,000 (monomer), 160,000 (dimer), 300,000 (tetramer) or 600,000 (octamer), whereas haemagglutinating activity was only found for the glycoproteins aggregated in a high mol. wt. (approximately 10(6) daltons) form. The isolated glycoproteins contained two subunits revealed by sodium dodecyl sulphate polyacrylamide gel electrophoresis and three distinct antigenic components revealed by rocket immunoelectrophoresis. Different treatments of the glycoproteins after their isolation altered their structure. Consequently either neuraminidase and haemagglutinating activities were signicantly reduced, or one of these activities was not expressed.

Antigens, Viral↗
PubMed1977

Enhancement and stabilization effect of EDTA on Sendai virus neuraminidase activity.

EDTA was found to enhance, and exert a stabilizing effect on, Sendai virus neuraminidase activity. The effect was dependent on the molecular form of the enzyme and on the nature of the substrate. The "native form" (enzyme bound to the virions) was less influenced than the "mixed form" (enzyme separated from the surface of virions together with other glycoproteins), which in turn was less influenced than the purified enzyme. On the other hand, the stimulation by EDTA of neuraminidase-induced hydrolysis of fetuin was higher than that of ovomucoid. The kinetic data obtained indicate that EDTA modifies the enzyme in such a manner that the affinity of the substrate for the enzyme is increased.

Calcium↗
PubMed1975

Specific cleavage of Sendai virus nucleocapsid protein subunits during virus storage.

The alteration of whole Sendai virus and especially of its nucleocapsid polypeptides, during storage of the virus at 4 degree C in the allantoic fluids in which it was cultivated, has cultivated, has been studied by sodium dodecyl sulfate gel electrophoresis. During virus storage the nucleocapsid protein subunits with a molecular weight of 60,000 and the putative inner envelope protein with a molecular weight of 38,000 were mainly affected. Both virus components were partially degraded to smaller components. Examination of nucleocapsids isolated from "stored" virus showed that, in addition to the 60,000-molecular weight polypetide component, a smaller polypeptide component with a molecular weight of 46,000 appeared. The relative proportion of the small component increased with the storage period: a kind of specific conversion of large to small components occurred during storage. Since viruses kept in the absence of allantoic fluids revealed no similar modifications of their polypeptides, we concluded that a cellular component present in the allantoic fluids - very likely of enzymatic nature - is responsible for the observed cleavage of virus polypeptides.

Body Fluids↗