Influence of the extent of haemoglobin hydrolysis on the digestive absorption of haem iron in the rat. An in vitro study

This study was designed to assess the haem-peptide interactions which occur during progressive haemoglobin hydrolysis by digestive enzymes and their r elationship with haem iron digestive absorption. The behaviour of different haemoglobin hydrolysates was studied using the Ussing chamber model. Hydro lysates were produced from enzyme digestion of bovine haemoglobin at pH 3 b y pepsin and at pH 10 by subtilisin. Samples with increasing degrees of hyd rolysis (0-15%) were studied. Biochemical assays (pyridine haemochromogen m ethod and UV absorption spectra) were used to follow haem solubility and ha em-peptide interactions in samples. Increasing the hydrolysis level of haem oglobin was associated with an enhanced iron uptake; the highest uptake rat e was reached between 8 and 11% of globin hydrolysis, whichever enzyme was used. The mechanisms rendering iron soluble and available differ between th e two enzymes. The comparison between biochemical acid absorption data sugg ests that the formation of soluble peptide-haem complexes was not sufficien t to enhance haem iron absorption, since globin-bound iron is poorly absorb ed; an efficient absorption occurred only when haem was loosely bound to lo w molecular weight peptides.