Both sucrose and raffinose are broken up outside of the cell by the same enzyme, invertase. Sucrose generates glucose and fructose that can be immediately transported into the cell and assimilated. Raffinose leads to fructose and melibiose. The latter is broken up by another enzyme, melibiase, which is not present in all lab strains. As a matter or fact, the degradation of raffinose will yield less amount of fermentable sugars (33%) in lab strains than sucrose (100%) and therefore it can be considered a poorer carbon source. Neither sucrose nor raffinose should lead to a major repression of the GAL genes.
Having said this, I don't know why some labs prefer sucrose over raffinose or mixtures of both. An alternative to sugars is the use of respiratory carbon sources, such as glycerol or ethanol. I particular find that cells grow better in a mixture of the two (3% glycerol and 1% ethanol) than on any of them alone.
Hope this was helpful,
Postdoc in Nyström's lab
Dept. Cell and Molecular Biology
University of Gothenburg
>From Kerry Geiler <kgeiler from gmail.com>
Sent Sat 5/24/2008 12:50 AM
To yeast from magpie.bio.indiana.edu
Subject [Yeast] Raffinose versus Sucrose
I have a question about whether yeast grow better in sucrose and raffinose or a combination of both. I am using galactose induction, so I cannot grow my strains in glucose. I have inquired with many nearby labs and some use 2% sucrose, some use 2% raffinose, and some use 2% sucrose, 1% raffinose. However, none of these labs can tell me why they made this decision (it seems to be a part of their lab culture). Does anyone know the differences between yeast growth in sucrose vs raffinose? Do either of these sugars inhibit metabolism of the other sugar? Any information that will inform my decision of which sugar to choose would be greatly appreciated. Thanks!
kgeiler from gmail.com (mailto:kgeiler from gmail.com)
Yeast mailing list
Yeast from net.bio.net (mailto:Yeast from net.bio.net)
-------------- next part --------------
An HTML attachment was scrubbed...