35SMet, 35SCys or 35SCys/Met ?

fdaniels at BIOSCI.CBS.UMN.EDU fdaniels at BIOSCI.CBS.UMN.EDU
Fri Sep 29 08:51:22 EST 1995

imbeaud at wotan.ens.fr (Sandrine Imbeaud) wrote:

>I would like to evaluate the stability of a recombinant protein expressed
>in CHO cells, and measure rates of secretion. So, I need to process pulse
>and pulse-chase protocols. 
>What radioactive amino acid is more frequently used in these experiments.
>My protein only contains 3 Methionine and 12 Cysteine. Is 35SCys the best
>choice or 35SMet, is it necessary to use simply a mix 35SCys/Met ? I know
>that some firms prepare ready mix of 35SCys/Met : Amersham (ProMix (35S)),
>ICN (Tran35S-label) and NEN (Expre35S35S (35S) Protein Labelling Mix).
>Have you already test them ? Somebody told me that the background of
>ProMix (35S) was more important than Tran35S-label one. Is that true ?
>What would be the advantages to use a mix rather than a radioactive amino
>acid ? 


The 35S Cys/Met mixtures are an economical option for general protein
labelling as they are hydrolysates of E. coli yeilding approximately
75% Met/25% Cys.  Purified amino acids simply cost more money.  Since
your goal is to label protein in vivo containing both Cys/Met it would
be to your advantage to use the mixtures as far as generating high
specific activity products at a low cost is concerned.  Although many
protocols require the pure amino acids it appears that yours does not.
Good luck.
Frank Daniels
Minneapolis Medical Research Foundation
Minneapolis MN 55404
Email: fdaniels at biosci.cbs.umn.edu
Voice: (612)-347-5834

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