The biology of lactoferrin
Structure, iron binding, and the mechanisms that are genuinely established rather than merely proposed.
Lactoferrin is a single polypeptide chain of roughly 80 kilodaltons, folded into two globular lobes of similar architecture. Each lobe carries a binding site that holds one ferric iron ion, together with a carbonate ion, and holds it far more tightly than the related serum protein transferrin does.
That binding is the origin of most of what the protein is known for. The protein is not confined to one species. Cattle make their own version, and the two are 69 percent identical with different sugar chains attached, which is why human lactoferrin has to be made recombinantly before anyone can give it to a patient, and why the three trials that have done so sit apart from the rest of the literature.
Pages here cover the structure, the binding chemistry, where the protein is produced and released, and which of the proposed mechanisms have support beyond a single laboratory. That last question has an answer worth stating early, and the page on what lactoferrin does sets it out as a table: of eight functions commonly attributed to the protein, one was demonstrated in the purified molecule, three in human cells or human milk, three in animals or cell preparations, and one in bacterial culture.
Storage in neutrophil granules has a clinical use of its own. Neutrophils migrating into the intestinal wall carry lactoferrin with them and it ends up in stool, which is the basis of the fecal lactoferrin assay. Measured against endoscopy, its sensitivity for active disease is about 0.82, and it is the more specific of the two common stool markers while calprotectin is the more sensitive.
The definitional entry, what lactoferrin is, carries the structural detail: the 1989 crystallographic refinement of the human protein, the four residues that coordinate each iron atom, the measured concentrations in human and bovine milk with the assay behind each figure, and the antibacterial peptide that works without iron at all.
- What does lactoferrin do? Eight functions, each placed at the level where someone actually measured it.
- Human lactoferrin Two proteins doing the same job, 69 percent identical, and the human one is far the harder of the two to get hold of.
This page reports published research. It is general information, not medical advice, and not a recommendation to take anything. Lactoferrin supplements are derived from cow's milk and are unsuitable for anyone with a milk protein allergy. Anyone who is pregnant, breastfeeding, treating an infant, or managing a diagnosed condition should speak to a clinician first.