Indispensability of Iron-bound Chick Transferrin for Chick Myogenesis in Vitro

Myotrophic activity of highly purified chick transferrins (Tfs) to chick primary myogenic cells has been studied in a culture medium containing horse serum. Iron-binding to Tfs is indispensable for the activity. The removal of iron from Tfs gives rise to a complete loss of the activity and it is restored by iron-rebinding depending on the amount of bound iron. This result, combined with other physicochemical and immunological data, strongly, confirms that the myotrophic activity is exerted by the Tfs themselves, not by a contaminating material(s). It has been found that culture medium containing horse Tf which seems inadequate for the study of the biological effects of Tfs is, however, suitable for studies on chick Tfs, since horse Tf is inactive in promoting chick myogenesis. Terminal sialic acid residues are unrelated to myotrophic activity since Tfs with different numbers of residues (0, 1, and 2 moles/Tf molecule) are comprable in their activities. The mechanism of Tf action on cells and contradictions among previous papers as to the requirement of Tf for cell growth have been discussed from the viewpoint of an iron-donor with class-specificity.