OBSERVATIONS WITH A RESIDUALIZING LABEL IN USE TO MAP THE CATABOLIC SITES OF PLASMA-PROTEINS

Rat albumin, immunoglobulin G, transferrin, and aglycotransferrin were prepared for the comparison of their sites of degradation in rats. Io dotyramine-cellobiose was used as the residualizing label and a tyrosi ne-iodinated portion of the corresponding protein was used as the mark er of extracellular undegraded protein. Each protein yielded a distinc t distribution (or map) of catabolic activity throughout the body when expressed as percent dose accumulated per gram of tissue. The maps fo r albumin and transferrin were broadly comparable, whereas those for i mmunoglobulin G and aglycotransferrin were markedly different. As a wh ole entity, the liver appeared to top the list of organs/tissues contr ibuting to the degradation of albumin and transferrin. Additional expe riments aimed at facilitating the interpretation of results with resid ualizing labels were carried out with denatured albumin, asialofetuin, and human asialotransferrin type 3. These showed that various types o f cells retained the label for markedly different periods of time. We feel, therefore, that the technique is more suited for making comparat ive measurements than for obtaining degradation rates as absolute valu es in a given anatomical location.