Further isotopic studies on haemoglobin formation in the rat and rabbit

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Abstract
The incorporation of alpha-C14-glycine into the protoporphyrin and globin moieties of the hemoglobin of rats and of a rabbit was detd. at various intervals after admn. of glycine. Labelled valine was also admd. to the rats. After intervals greater than 24 hrs. the molecular radioactivity of protoporphyrin was approx. 8 times greater than that of the glycine isolated from the same sample of hemoglobin, in agreement with current theories of heme synthesis. After shorter intervals smaller values were obtained. Possible explanations are discussed. Valine was also isolated from the "end-groups" and remainder of the rat hemoglobin molecule. The radioactivities of both fractions were identical at all intervals of time. The implications of this finding are discussed. The relative radioactivity of glycine to that of valine isolated from hemoglobin and from the heterogeneous protein "stromatin" decreased as time went on. This is attributed to increasing dilution of radioactive glycine by endogenous synthesis. The isotope contents of glycine and valine isolated from "stromatin" and hemoglobin were compared. It is concluded that stroma proteins are formed earlier and are for the most part as metabolically inert as hemoglobin.
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