Leptin is a 16,000-Da protein which is secreted by fat but acts within the brain to regulate
adiposity. Our Peptides Classic addressed the mystery of how such a large molecule could
negotiate the blood–brain barrier (BBB), a structure which normally excludes proteins from
the brain. We found that leptin was transported across the BBB by a saturable transport
system. This finding was important to understanding how satiety-related peptides and
proteins worked, but it was also important to the concept that the BBB is a regulatory …