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K B Tan

Publications and source records attributed to K B Tan.

At least 73 records · Page 4Linked to original sources
PubMed1974

Virion-bound protein kinase in Semliki forest and Sindbis viruses.

Semliki forest virus and Sindbis virus (Alphaviruses belonging to the togavirus group) grown in BHK-21 cells possessed very low levels of virion-associated protein kinase activity. For comparison, vesicular stomatitis virus, also grown in BHK-21 cells, contained a virion-bound protein kinase which had a specific activity 80 times greater than that of the Alphaviruses. The Alphavirus protein kinase was unmasked by the nonionic detergent Nonidet P-40 but was not activated by cyclic nucleotides. Phosvitin was the best exogenous phosphate acceptor for assaying the viral enzyme in vitro. Phosphoprotein phosphatase activity was also detected in the Alphaviruses. Both in vivo and in vitro, all of the viral structural polypeptides were phosphorylated, and the phosphorylated amino acids were found to be serine and threonine. The viral nucleocapsid protein was about four times more efficient as a phosphate acceptor than were the envelope proteins. From 33 to 50% of the total protein kinase was bound to the viral nucleocapsid, and the specific activity of this enzyme was 4 to 10 times greater than that associated with the viral envelope.

Animals↗
PubMed1974

Phosphate acceptor amino acid residues in structural proteins of rhabdoviruses.

Partial acid hydrolysates of the [(32)P]phosphate- or [(3)H]serine-labeled proteins of purified vesicular stomatitis, rabies, Lagos bat, Mokola, or spring viremia of carp virions and of purified intracellular nucleocapsids of these viruses have been analyzed by paper electrophoresis for the presence of phosphorylated amino acids. Both phosphoserine and phosphothreonine, with the former predominant, were present in virion and nucleocapsid preparations that contained phosphoproteins. An exception was the fish rhabdovirus, which contained only phosphoserine. When vesicular stomatitis or rabies virus proteins were phosphorylated in a cell-free system by the virion-associated protein kinase and analyzed for the presence of phosphorylated amino acid residues, phosphoserine was again found to be more abundant than phosphothreonine. After in vitro protein phosphorylation, another phospho-compound, possibly a third phosphoamino acid, was detected in the partial acid hydrolysates of these viruses.

Amino Acids↗
PubMed1973

Phosphorylation of simian virus 40 proteins in a cell-free system.

We have shown previously that all the structural proteins of simian virus 40 (SV40) are phosphoproteins. Virus phosphorylated in vivo could be further phosphorylated with exogenous cellular protein kinases in a cell-free system containing gamma-(32)P-ATP as phosphate donor. In intact infectious virus only polypeptides 1 and 2 (mol wt 49,000 and 40,800, respectively) were further phosphorylated in vitro. However, when infectious SV40 was partially disrupted, treated with nucleases, and then phosphorylated in vitro, all five structural polypeptides accepted additional phosphate groups. Similarly, all polypeptides of intact empty capsids, derived from infected cells, were further phosphorylated in vitro. Phosphorylation of empty capsids and infectious SV40 in vitro was enhanced from 4- to 11-fold after prior treatment of virus with alkali. The phosphate group was linked only to serine residues of the viral polypeptides phosphorylated both in vitro and in vivo.

Adenosine Triphosphate↗
PubMed1972

Structural proteins of simian virus 40: phosphoproteins.

All five structural polypeptides of infectious simian virus 40 grown in African green monkey kidney cells were found to be phosphorylated. The polypeptides with the largest and smallest molecular weights are phosphorylated to a somewhat lower extent than the other polypeptides. The protein moiety of "empty" virus, which is essentially devoid of deoxyribonucleic acid, exhibited a degree of phosphorylation similar to that of infectious virus. In the major polypeptide (molecular weight: 49,000), the phosphate appears to be bound to the seryl or threonyl residues, or both. The nature of the phosphate-polypeptide bond in the other viral polypeptides remains obscure.

Amino Acids↗
PubMed1972

Binding of deoxyribonucleic acid-dependent deoxyribonucleic acid polymerase to poxvirus.

Poxvirus has a deoxyribonucleic acid polymerase activity that remains associated with the virus despite repeated centrifugation through sucrose gradients. Highly purified poxvirus preparation can adsorb deoxyribonucleic acid polymerase from cytoplasmic extracts of cells containing such an activity. These results indicate that caution must be used in assuming that an enzyme associated with a purified virus is necessarily an integral part of the virion.

Adsorption↗
PubMed1971

Proteins of a polyhedral cytoplasmic deoxyvirus. 3. Structure of frog virus 3 and location ov virus-associated adenosine triphosphate phosphohydrolase.

The adenosine triphosphatase associated with frog virus 3 shows high specificity for ATP or deoxyadenosine triphosphate and appears to be distinct from the corresponding activity in host cells, poxvirus, or reovirus. The enzyme activity is probably integrated into virus particles since it is firmly associated with subviral particles produced when approximately 50 to 60% of the outer viral protein is removed by detergent treatment. The occurrence of adenosine triphosphatase activity within three unrelated viruses suggests that adenosine tryphosphatase might be a necessary function for most viruses that replicate in the cell cytoplasm.

Adenosine Triphosphatases↗
PubMed1970

Electron microscopy of cells infected with Semliki forest virus temperature-sensitive mutants: correlation of ultrastructural and physiological observations.

Cells infected at the permissive temperature with three temperature-sensitive mutants of Semliki Forest virus were not significantly different in appearance from cells infected, at either the permissive or nonpermissive temperature, with wild-type virus. Virus particles, nucleocapsids, spherules, and tubules were seen in the cytoplasm. But replication of the mutants was inhibited in cells infected at the nonpermissive temperature. This was evidenced by the absence of virus particles and nucleocapsids (except in one case) and the absence or limited production of spherules and tubules. These observations are discussed with reference to the physiological defects of the mutants.

Animals↗
PubMed1970

Effect of rifampicin on poxvirus protein synthesis.

Poxvirus strains differ with respect to the effect of rifampicin on viral protein synthesis. Rifampicin severely depressed vaccinia-directed protein synthesis but had little effect on the rate of cowpox-directed protein synthesis, including one late virus-induced enzyme. The spectrum of polypeptides synthesized in cowpox-infected cells was similar in the presence or absence of rifampicin except for one significant difference. After removal of rifampicin, viruslike particles assembled to some extent, even when protein synthesis was inhibited by cycloheximide. However, reversal was more extensive if protein synthesis was allowed.

Centrifugation, Density Gradient↗
PubMedDate not supplied

Implant-abutment screw joint preload of 7 hex-top abutment systems.

This study measured the screw joint preload of the implant-abutment interface for 7 common hex-top abutment systems. Increasingly, prosthetic designs are utilizing a direct prosthetic connection to the implant, placing the implant-abutment screw joint under direct functional loads and moments. Sufficiently high screw joint preloads are required to maintain screw joint integrity and confer clinical longevity to implant prosthetic components to prevent such complications as abutment screw loosening and screw fracture. Strain-gauged abutment load cells were calibrated to measure screw joint pre-load at the implant-abutment interface. Torque delivery by electronic torque controller was varied at low- and high-speed settings. At manufacturer's recommended torques, the overall mean preload measured was 181.6 +/- 60.0 N for the Nobel Biocare Standard abutment, 291.3 +/- 41.2 N for the Nobel Biocare EsthetiCone abutment, 456.5 +/- 44.0 N for the Nobel Biocare MirusCone abutment, 369.7 +/- 32.9 N for the 3i Titanium Abutment post, 643.4 +/- 143.1 N for the Nobel Biocare CeraOne abutment, 536.3 +/- 68.6 N for the Nobel Biocare "Gold Cylinder to Fixture" abutment, and 556.9 +/- 145.6 N for the Nobel Biocare TiAdapt abutment. Analysis of variance revealed significant differences between abutment systems (P < .001) and between torque driver speed settings (P < .001). Implant-abutment screw joint preload of external-hex implants is dependent on abutment design, screw diameter, material, tightening torque, and torque controller speed.

Analysis of Variance↗