Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2001
Publication Date: 2/1/2002
Citation: SWAIN, J.H., TABATABAI, L.B., REDDY, M.B. HISTIDINE CONTENT OF LOW MOLECULAR WEIGHT BEEF PROTEINS INFLUENCES NONHEME IRON BIOAVAILABILITY IN CACO-2 CELLS. JOURNAL OF NUTRITION. 2002. 132:245-251.
Interpretive Summary: Absorption of iron in humans depends on an individual's iron status, iron intake, and its bioavailability. Nonheme iron constitutes the major source of iron, and its absorption is influenced by many factors. The enhancing effect of meat on iron absorption is attributed to unknown factor(s), known as meat factors. Only beef, lamb, liver, pork, poultry and fish enhance nonheme absorption. Egg, cheese, milk, and ovalbumin proteins do not. The research described in this work has identified meat factors that may play a role in enhancing the absorption of nonheme iron. These factors are short peptides with molecular weights of 1,000 to 7,000 that contain the amino acid histidine.
Technical Abstract: The objective of this study was to isolate and characterize beef muscle proteins that enhance nonheme iron availability. Beef sirloin was cooked, lyophilized, and reconstituted with water prior to in vitro digestion. Following centrifugation, the digest supernatant was sequentially ultrafiltered using 10K and 1K molecular weight cut-off membranes. Nonheme eiron bioavailability was assessed by Caco-2 cell monolayer 59Fe uptake using an extrinsic labeling method. All ultrafiltration fractions significantly (P<0.0001) increased iron solubility at pH 6.0, compared to the blank. However, iron uptake only in the presence of the 1-kDa retentate (1KR) was significantly (P<0.001) greater than the blank. Therefore, the 1KR was chosen for further analysis. Immobilized metal affinity chromatography (IMAC) of the 1KR yielded four fractions: three distinct (F1, F3, F4) and one comprised of a few closely associated peaks (F2). All four IMAC fractions significantly (P<0.001) increased (2- to 5-fold) iron solubility at pH 6.0, compared to the blank. Iron uptake with F2 and F4 was significantly greater than the blank (P<0.001 and P<0.05, respectively). Gel electrophoresis and Matrix-Assisted Laser Desorption/ Ionization analysis illustrated that F1-F4 contained many peptides ranging from 1-7 kDa. Amino acid composition analysis revealed that histidine concentration increased progressively from F1-F4, corresponding with a general, but not parallel, increase in iron solubility and uptake. Our results suggest that the enhancement of nonheme iron absorption by beef may be due to peptides produced during gastrointestinal digestion and that histidine content may be important.