growth media question - (Nov/02/2004 )

To make LB liquid I'm using tryptone peptone as one of the ingredients. Is that the same as just tryptone? Would this interfere with growth or protein expression?

That's a bit tricky. Depending on manifacturer tryptone is also called Peptone 140 and is tryptic digested casein. Peptone is also called peptone 140 and it's pancreatic digested gelatin, I think.
Basically you should check your manicacturer try to find out precisely what it is.
Possibly the ingredient you are using is a mix.
And yes changes in the medium can result in growth differences (though depending on your species/strain it is possible that they are not visible) and almost always leads to a change in the proteome. If you want to purify a specific protein it might not be important (especially for instance if working with an overexpression vector). However whole proteome approaches (2d gel for instance) are very sensitive to changes in medium composition.

I appreciate the info you gave me. I've by trying to purify a protein in a pRSET vector and found that I get protein production even before I induced expression with IPTG. I'm trying to go through a number of different things to see if I can isolate where my problem may be coming from. Thanks again

OK overexpression then. That's a different issue. Most overexpression vectors are kinda leaky, that is even w/o induction a certain amount of transcripts can be found.
Alternatively you could have galactose contamination (doubt it, though).