l - People

mucous secretions. It has broad spectrum antibacterial properties ascribed to an 18-
residue loop near the N-terminus. The antibacterial activity is observed when lactoferrin
is complexed with iron (but not in the apo form) or after the protein has been digested
with one of several pepsins or proteases. Significant amounts of lactoferrin enter the
intestinal tract of mammals and there is evidence that lactoferrin may be absorbed from
the lumen of the small intestine into enterocytes. Lactoferrin concentration in human
milk appears to be independent of maternal iron status. For these reasons, it appears that
ingested lactoferrin plays a significant role in protecting newborns from infectious
disease. Separate from this role as an antibiotic, lactoferrin seems to regulate the
absorption and excretion of iron in infants since those fed hLF-free milk absorbed more
iron than those fed unaltered milk. Further, hLF is found in the feces of infants at
substantial concentrations.
The hinge bending motion of lactoferrin has been studied in detail. The protein consists
of N- and C- terminal lobes which are highly homologous and are presumed to have
arisen from gene duplication. Each lobe is further subdivided into two domains, N1 and
N2, and C1 and C2. In the iron-free form, a deep cleft appears between N1 and N2. No
such cleft appears in the C-lobe either in the iron free or iron bound form, but this is
believed to be an artifact of crystallization. In the iron-bound form, N1 and N2 are close
together about a common hinge, located between residues 90 and 91, and 250 and 251
according to Gerstein et al. This is in perfect agreement with the independent annotation
made in this work.
212