OD at 320nm

Achim Recktenwald achim at ibex.ca
Mon Aug 12 13:46:43 EST 1996

Edouard Lauzier wrote:
> I read that at 320nm neither protein or nucleic acids absorb.  In my
> spectrophotomer instruction book they're saying that substracting the OD
> value at 320 from the other OD will then take account for the background .
> but...
> It doesn't necessary mean that whatever absorb at 320 will absorb too at
> 260.  So by substracting the 320 value from the 260, am I not
> underestimating my RNA levels in my sample ? ( that is in the case the
> background is less at 260 or even nil because I have absolutly no proof
> that it absorb the same at 320 and 260 ! )...
> and if it's not proteins or nucleic acids, then what can it be that absorb
> at 320 ???
> Thank you...
> --
> Edouard Lauzier, B.Sc.                           elauzier at fse.ulaval.ca
> Physical Activity Science Laboratory       (418) 656-2131 #2929
> (Laval University)  G1K 7P4

Phenolic compounds; I am using a spectrophotometric enzyme assay for the
detection of 4-hydroxy-trans-cinnamic acid and measure at 340 nm. The
compound is produced during the reaction of tyrosine with phenylalanine
ammonia lyase. At 320nm the absorption would be even higher, but at that
wavelength I can still detect some interference by tyrosine.


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