[RASMB] shift in absorbance

[Kristian Schilling]

Dear all - I am forwarding this request from Antje and Helmut as they are 
encountering problems in addressing the RASMB server. If you wish to send 
any answers directly to Antje, please use her email address given here: 
voelkel at mpigk.mpg.de. Answers via RASMB will be received as well. Best, 
Kristian

>Dear RASMB readers and writers,
>
>I was measuring an elongated, charged protein by AUC in titanium 
>centerpieces with quartz windows. My question is orientated in the 
>absorbance direction.
>
>The Mw of the Monomer is ~20kDa. In basic environment it builds 10 nm 
>particles but I could not observe any movement on the way to maximum 
>velocity. Partly the sample might be aggregated in Buffer with pH of 7.76. 
>In the reference sector the buffer composition was the same like in the 
>sapmle sector. Tris buffer (0.133mM) should not absorb at 273 nm, like I 
>found in the list of Borries.
>
>As I cleaned the cells, I saw, that the sample is attached to the windows, 
>this effect is stronger in water than in buffer.
>
>For better understanding I attached a pdf file of the wavelength scans at 
>1200 nm and the radial scans of the sedimentation at 60000 rpm.
>
>I was wondering about:
>
>a) the difference in the wavelength spectra at different pH values, 
>aggregates should be sedimented already
>b) the shape of the scans in buffer(Why is the absorbance at the meniscus 
>negative in the beginning and then increasing? Is it because the protein 
>takes counterions with it, and a negative signal appeyars? Is there a 
>boundary?)
>c) if there is any interaction known of titanium centerpieces and proteins
>
>I would be glad to get some answers
>best regards
>Antje
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