Abstract
The serum of tumour-bearing rats has been tested to determine if there is any protein shedding from the plasma membrane of the tumour cells. Both immunological and enzymological approaches have been employed. Methods for isolation of plasma membrane fragments for two different hepatomas have been developed. Plasma membrane fragments from the less rapidly growing (WDA) hepatoma are recovered in two distinct size classes which, it is suggested, derive from two distinct areas of the plasma membrane which have been distinguished by electron microscopy. Plasma membranes from the more rapidly growing (UA) hepatoma appeared much more uniform both in morphological appearance and in cell fractionation experiments. An antiserum has been prepared against purified plasma membrane fragments from the 'UA' hepatoma. The reaction of this antiserum has been examined by crossed immunoelectrophoresis and the various proteins characterised by comparison with the reaction of the sera with anti-(rat serum) and antiserum prepared against the serum of tumour-bearing rats and normal liver plasma membrane. The results did not show extensive release of material from the tumour plasma membrane into the serum, although evidence was obtained for a complex containing material deriving from tumour plasma membrane together with host serum proteins. Enzymological methods have been used to study the 5'-nucleotidase and alkaline phosphatase enzymes in plasma membrane fragments and in serum. Evidence was obtained that the apparent 5'-nucleotidase activity of normal rat serum is largely due to a non-specific phosphatase. This was also suggested by gel filtration of serum on Sephadex G-200. Gel filtration of the serum of tumour-bearing rats did, however, give evidence for the presence of a very; high molecular weight complex which contains 5'-nucleotidase but with little if any alkaline phosphatase activity. This would be consistent with the complex deriving from the surface of tumour cells.