Protein wight in kDa - (Nov/16/2011 )

How to convert the number of amino acid of protein in its molecular weight in kDa.

It's not the number of amino acids what matter but the amino acids and their specific weight. You need the sequence and then you can use several tools to determine the molecular weight (eg. ProtParam Expasy).

papaver is correct but, back in school (mid 70s), we learned a quick and dirty method of determining an approximation of the number of amino acids in a protein (given the formula weight).

divide the formula weight of the protein by the average formula weight of an amino acid (in school they said ~100, other sources say ~120 (i think)).

therefore, a 60kDa protein will contain ~600 (or ~500, if using 120) amino acids.

of course, this does not take into account any post translational modifications.

also, of course, these are not publishable numbers. they are only for rough approximation.