Bob,
The Expasy site has several such programs (http://expasy.hcuge.ch/)
although the calculations are usally performed on proteins and then
"antigenic" peptides extracted from the plots.
Regards,
Dan L. Crimmins
Washington University School of Medicine
Dept. Pathology/Division of Laboratory Medicine
660 S. Euclid Ave., Box 8118
St. Louis, MO 63110
Phone: 314-454-8514; Fax: 314-454-5208
e-mail: crimmins@labmed.wustl.edu