(no subject)
Gregory Grant (ggrant@pharmdec.wustl.edu)
Wed, 3 Mar 1999 09:05:02 -0600
>Hello all,
>
>We ran amino acid analysis of some whey samples using our Beckman 6300,
>Sodium method, found 20% cysteine (ususal for this lot), but there was a
>lot of noise, so we decided to rerun the samples. A machine breakdown
>later, we rehydrolyze, on the assurance that our Ninhydrin is on the truck.
>The truck was slower than usual, so the samples and standards sat in the
>refrigerator dissolved in Na-S for five days. The latest analysis has no
>noise, nice baselines, but _no_ cysteine, and threonine levels had doubled
>from earlier. All the other results were within the range I might expect,
>considering that we were not happy with the earlier analysis.
>
>My question: Does cysteine break down in the fridge in Na-S? Does it
>break down into something that elutes with threonine?
>
>-laurey
>
>Weather Inconsequential: It was gorgeous yesterday, but the clouds have
>moved in today and the temperature is dropping. It seems like March again
>instead of May.
>Laurey Steinke
>Protein Structure Core Facility
>University of Nebraska Medical Center
>Omaha Nebraska, 68198-4525
>
>Phone (402) 559-6647
>FAX (402) 559-6650
>lsteinke@molbio.unmc.edu
Laurey,
Cysteine will oxidize to cystine with time after hydrolysis and
which elutes earlier on the column. Usually around Pro on ion exchange
systems (in the old days) but I suppose this can vary depending on your
system. This could accont for the increase at thr.
Greg
Gregory A. Grant
ggrant@pharmdec.wustl.edu