The bioavailability of iron added to different types of cows' milk formulas was studied using mono-isotopic and double-isotopic methods in 396 infants aged 5-18 mo. All the milk formulas were fortified with ferrous sulfate in concentrations varying between 10 and 19 mg elemental iron/liter. Iron absorption from low-fat milks and full-fat milks varied from 2.9 to 5.1%. A higher range of mean absorption, 5.9 to 11.3%, was observed in the same formulas with the addition of ascorbic acid at concentrations of 100 mg/l or higher (up to 800 mg/l), demonstrating its enhancing effect on iron absorption in fortified milks. The amount of milk fat, the addition of carbohydrates, or acidification did not seem to influence iron absorption.

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Classical molecular dynamics simulations of the d-Gln/Aquifex pyrophilus MurI and d-Glu/Aquifex pyrophilus MurI complexes have been carried out. Since the active site of the enzyme contains many charged and polar residues, several binding modes are possible. Thus, three very different stable conformations of the substrate analogue d-Gln have been found, and at least three binding modes are possible for the substrate d-Glu. These qualitative results give an explanation for the apparent disagreement between the d-Gln bound MurI X-ray crystal structure and the expected position and orientation of the substrate d-Glu in order to make it possible the assumed Cα deprotonation (by Cys70)/reprotonation (by Cys178) racemization mechanism.