RESUMO
There are three major methods for buffer exchange of proteins at industrial scale: size exclusion chromatography (SEC), tangential flow filtration (TFF), and countercurrent dialysis (CCD). In order to determine the optimal technology for a given process, a study was done to compare these technologies on a technological and economic basis. This comparison required that new mathematical models be developed which enable the common features of each unit operation to be directly compared. The new concept of a diavolume equivalent for SEC, defined as the inverse of the fractional loading, was also introduced to aid in this comparison. Variables that were examined for each unit operation included range of buffer exchange, dilution of protein solution, yield, buffer requirements, total operating time, throughput, plant space, capital, raw materials, and labor costs. It was found that TFF and CCD have a greater range of buffer exchange than SEC. TFF also provides the advantage that concentration of the protein can readily be accomplished in the same step. For processes of equal batch size and yield, TFF and CCD also provide a two- to five- fold improvement in each of the remaining variables. The major economic advantage in using TFF and CCD over SEC is the decreased plant size required for manufacturing and thus the longer term use of existing facilities. Situations where SEC (or CCD) would be favored over TFF are when protein denaturation occurs in TFF but does not occur in SEC. (c) 1995 John Wiley & Sons, Inc.
RESUMO
Breakdown of the blood-aqueous barrier was produced by infrared radiation (IR) at a heat flux from 24 to 44 J/cm2 in pigmented, but not in albino rabbits. Blood-aqueous barrier breakdown was inhibited by indomethacin and ketamine/xylazine anesthesia mixtures, but not by [D-Trp2,D-Pro7,9]-substance P. The degree of blood-aqueous barrier breakdown could be controlled by IR flux. Two models for accurate determination of the heat flux are presented.