Biomedical Engineering Reference
In-Depth Information
Mammary
cell
WAP promoter
tPA cDNA
transcription &
translation
Upstream
processing
tPA
Exported into milk
Acid Fractionation
Downstream
processing
Hydrophobic interaction
chromatography
Immunoaffinity
chromatography
Figure 5.2 The production and purifi cation of tPA from the milk of transgenic goats. (WAP promoter: murine
whey acid promoter). The downstream processing procedure yielded in excess of an 8000-fold purifi cation
factor with an overall product yield of 25 per cent. The product was greater than 98 per cent pure, as judged
by sodium dodecyl sulfate (SDS) electrophoresis
Pre-availability of commercial milking systems, already designed with maximum process
hygiene in mind.
Low capital investments (i.e. relatively low-cost animals replace high-cost traditional fermenta-
tion equipment) and low running costs.
High expression levels of proteins are potentially attained. In many instances, the level of ex-
pression exceeds 1 g protein/litre milk. In one case, initial expression levels of 60 g l 1 were
observed, which stabilized at 35 g l 1 as lactation continued (the expression of the
α 1 -antitrypsin
gene, under the infl uence of the ovine β-lactoglobulin promoter, in a transgenic sheep). Even at
expression levels of 1 g l 1 , one transgenic goat would produce a similar quantity of product in
1 day as would be likely recoverable from a 50-100 l bioreactor system.
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