I want to query the molecular weight of multiple proteins from R given uniprot ids. I thought of using biomaRt or UniProt.ws, but didn't see which field I should query.

There are online tools performing the calculation given a uniprot ID (PIR, ExPASy), but you have to manually enter the input and save the output.

I want the MW that appears in UniProt when looking in "Sequences" under Mass (for example for the entry http://www.uniprot.org/uniprot/Q9Z2Y8)
<p>On the uniprot site you can ask for the predicted mass column.</p>

<p>Click on the columns button. click on the check-box labeled mass under the sequence category.</p>

<p>Save, search for your accession using the syntax below and get tab delimited output back.</p>

<p>http://www.uniprot.org/uniprot/?format=tab&amp;query=accession:Q6GZX4&amp;columns=id,entry+name,mass</p>
