I have written a program to compute the possible peptides to correspond to
a given molecular weight. (In Modula 2 - Dave, you are not alone ;-). )
It was an exercise in programming, but not much else, since the number of
possible peptides for any given weight is astronomical.
For example, at your weight of 829, there are 4575 possible peptides within
a single mass unit. (between 828 and 830). And this is peptides of different
composition only, not sequence.
With sequence information, mass matching is very effective, but without it
the possibilities are too numerous. Amino acid composition would probably
help, but that too is usually unavailable.
Allen Delaney (allen at brc.ubc.ca)
Biomedical Research Centre, U.B.C., Vancouver, B.C. Canada, V6T 1Z3