THE EFFECT OF DIGESTIVE ENZYMES ON THE BINDING AND BACTERIOSTATIC PROPERTIES OF LACTOFERRIN AND VITAMIN B12 BINDER IN HUMAN MILK

Abstract. Samson, R. R., Mirtle, C. and McClelland, D. B. L. (University Department of Therapeutics and Clinical Pharmacology, The Royal Infirmary, Edinburgh, Scotland). The effect of digestive enzymes on the binding and bacteriostatic properties of lactoferrin and vitamin B12 binder in human milk. Acta Paediatr Scand, 69:517, 1980.—Human milk contains unsaturated lactoferrin and vitamin B12 binding protein. It has been suggested that these proteins may exert antibacterial effects in the intestine of the breast fed infant, but the effect of the intestinal environment on the antibacterial effect of these proteins has not been described. In this study human milk was treated with pepsin and trypsin and the influence of digestion on iron and vitamin B12 binding capacity, bacterial uptake of iron and vitamin B12 from milk and bacteriostatic effect was studied. Pepsin digestion had no effect on vitamin B12 binding capacity, or the ability of bacteria to take up vitamin B12, or the growth inhibitory effect on a vitamin B12 dependant strain. In contrast, pepsin digestion (or low pH alone) released iron from milk and abolished its bacteriostatic effect. Trypsin digestion slightly reduced the molecular size of the vitamin B12 binding protein without releasing free vitamin B12; the bacteriostatic effect on a vitamin B12 dependant organism was, however, abolished. In contrast, trypsin digestion did not affect iron binding or bacteriostatic effects attributable to lactoferrin. The findings support an in vivo bacteriostatic role for lactoferrin in the breast fed neonate's intestine but do not support a similar role for the vitamin B12 binding protein.