Effects of microwaves (0.9-2 GHz) on metalloproteins and electron-transfer reactions

Lactoferrin is a nonheme, member of the transferrins family, iron-binding and irontransporter protein originally isolated from milk, but since identified in a variety of mammalian secretions, such as lachrymal fluid. It has also been shown to be a major iron-binding protein of exocrine secretions such as bile, pancreatic juice and small intestinal secretions. It consists of single polypeptide chain, folded into two globular lobes, each with one iron binding site and these sites appear noninteracting. The complete amino acid sequence of human lactoferrin has been determined and found to contain 703 amino acid residues, with molecular weight 82.6 KDa. Iron binding to lactoferrin occurs concomitantly with the bonding of two bicarbonates anions, a process essentialfor the ligation of iron to the protein active side. This iron-bicarbonate-protein complex develops a salmon colour, with an absorption maximum between 460 and 470 nm.
There is a notable degree of internal homology between the two lobes (residues 1-338 and 339-703, respectively), which demonstrates 125 (37%) identical amino acid residues in the corresponding portions.
Lactoferrin is a basic glycoprotein with an isoelectric point of 8.7 which contains 41% α-helix and 24% β-sheet. Two glycans, attached to protein through N-glycoside linkages, are nevertheless structurally heterogeneous and differ from those of other transferrins. The precise role of these glycans has not been established, and their removal is said to have no apparent effect on lactoferrin functions and properties, such as receptor of binding. However, this assumption has been contested by other works in which the glycans appear to have a role in receptor binding. It is known that lactoferrin is remarkably resistant to proteolytic degradation by trypsin and trypsin-like protein and this property facilitates neonatal absorption of lactoferrin from maternal milk. Iron-saturated form is more resistant to proteolytic degradation than apoform. Lactoferrin binding ability is not limited to iron but copper, zinc, manganese, gallium, and possibly vanadium as well are known to be substrate for this molecule. The iron binding domains consist of β-sheets as well as α- helices. Several observations, such as spectrophotometric titration of tyrosine, treatments with compounds related to tyrosine, pH variations of apolactoferrin, fluorescence, NMR and circular dichroism, indicate that the binding sites may contain histidine, tyrosine and tryptophans.
Some controversy still exists about to the exact role and mechanism of action of lactoferrin. It has now been shown that lactoferrin plays a role in the host defense mechanism, as well as, in the iron metabolism. Lactoferrin, in addition to its bacteriostatic function, can also exert a bactericidal effect and can curb the proliferation of other microbes such as fungi and viruses. It seems this protein may promote iron absorption in breast-fed infants. In fact, it has been observed there are a higher lactoferrin concentration and higher iron availability in human than in bovine milk.
However the major role of lactoferrin in iron metabolism would appear to be in the control of iron availability. Finally an antithrombotic function has also been ascribed to lactoferrin.