EFFECT OF MYOFIBRILLAR MUSCLE PROTEINS ON THE IN-VITRO BIOAVAILABILITY OF NONHEME IRON

It is well established that the bioavailability of non-haem iron from foods is enhanced by the presence of meat. However, the nature of the promoter in meat has not yet been characterised. The present study was designed to compare the effects of the myofibrillar protein fractions on the bioavailability of non-haem iron in an attempt to identify the 'meat factor'. Rabbit skeletal muscle was fractionated and whole musc le, myofibrillar protein, myosin and actin were isolated. Myosin was s ubjected to selective proteolysis with chymotrypsin and the heavy mero myosin, light meromyosin, rod region and head region were prepared. Pr otein fractions (1 g) were incorporated into 100g semi-synthetic liqui d meal and the in vitro dialysability of iron was determined. Egg albu min was used as a reference protein. When compared with egg albumin, a ll protein fractions significantly enhanced iron dialysability, except for light meromyosin which was inhibitory. Myosin had a greater enhan cing effect than actin and, within myosin, the enhancing effect was gr eatest for the heavy meromyosin fraction. The enhancement appeared to coincide with the known distribution of cysteine residues in the myofi brillar proteins. The presence of the sulphydryl blocking agent, N-eth ylmaleimide (NEM), in meals containing myosin reduced iron dialysabili ty in a dose-related manner, but NEM had only a small effect in meals containing actin. Meanwhile, incorporation of cysteine into meals cont aining actin increased iron dialysability. The present results suggest that the enhancement of non-haem iron dialysability by meat is associ ated with myosin, in particular, with the heavy meromyosin region. Pep tide fractions rich in cysteine residues, probably constitutes the 'me at factor'.