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D I Wang

Publications and source records attributed to D I Wang.

63 records · Page 4Linked to original sources
PubMed1967

Effect of Microwaves on Escherichia coli and Bacillus subtilis.

Suspensions of Escherichia coli and Bacillus subtilis spores were exposed to conventional thermal and microwave energy at 2,450 MHz. The degrees of inactivation by the different energy sources were compared quantitatively. During the transient heating period by microwave energy, approximately a 6 log cycle reduction in viability was encountered for E. coli. This reduction was nearly identical to what is expected for the same time-temperature exposure to conventional heating. Heating of B. subtilis spores by conventional and microwave energy was also carried out at 100 C, in ice and for transient heating. The degree of inactivation by microwave energy was again identical to that by conventional heating. In conclusion, inactivation of E. coli and B. subtilis by exposure to microwaves is solely due to the thermal energy, and there is no per se effect of microwaves.

Journal Article↗
PubMedDate not supplied

Experimental collision efficiencies of polymer-flocculated animal cells.

The determination of particle collision kinetics is useful to decouple the effects of process parameters on individual events in flocculation. This paper discusses the effects of flocculation conditions on the collision efficiency of ATCC strain CRL 1606 hybridomas flocculated with poly-L-histidine. Experimental determinations of the collision efficiency of cells in Couette flow are presented over a range of experimental conditions. The collision efficiency correlates with the cell zeta potential to the -2.4 power at high surface coverage, consistent with literature results in latex systems. At low coverage, accounting for the distribution of polymer on the cells corrects for deviation from the high-coverage behavior. Collision is dependent on the hydrodynamic environment as well. At high surface coverage, collision efficiency is weakly dependent on hydrodynamic conditions and follows a dependency on the shear rate and viscosity to the -0.32 power. This is consistent with ionic coagulation theory. At low surface coverage, the collision efficiency is strongly dependent on the viscous fluid forces. The results versus both dose and shear rate over the entire range of surface coverages are consistent with weak intercell bonding. Collision kinetics in the presence of high molecular weight dextrans show steric hindrance to cell collision.

Animals↗
PubMedDate not supplied

Transient association of the first intermediate during the refolding of bovine carbonic anhydrase B.

Many proteins which aggregate during refolding may form transiently populated aggregated states which do not reduce the final recovery of active species. However, the transient association of a folding intermediate will result in reduced refolding rates if the dissociation process occurs slowly. Previous studies on the refolding and aggregation of bovine carbonic anhydrase B (CAB) have shown that the molten globule first intermediate on the CAB folding pathway will form dimers and trimers prior to the formation of large aggregates (Cleland, J. L.; Wang, D. I. C. Biochemistry 1990, 29, 11072-11078; Cleland, J. L.; Wang, D. I. C. In Protein Refolding; Georgiou, G., De-Bernardez-Clark, E., Eds.; ACS Symposium Series 470; American Chemical Society: Washington, DC, 1991; pp 169-179). Refolding of CAB from 5 M guanidine hydrochloride (GuHCl) was achieved at conditions ([CAB]f = 10-33 microM, [GuHCl]f = 1.0 M) which allowed complete recovery of active protein as well as the formation of a transiently populated dimer of the molten globule intermediate on the refolding pathway. A kinetic analysis of CAB refolding provided insight into the mechanism of the association phenomenon. Using the kinetic results, a model of the refolding with transient association was constructed. By adjusting a single variable, the dimer dissociation rate constant, the model prediction fit both the experimentally determined active protein and dimer concentrations. The model developed in this analysis should also be applicable to the refolding of proteins which have been observed to form aggregates during refolding. In particular, the transient association of hydrophobic folding intermediates may also occur during the refolding of other proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗