Human tumor cell membrane glycoprotein associated with protein kinase activity

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Abstract
A mouse MAb3 50H.19 raised against the human melanoma cell line MEL‐T binds to carcinoma cell lines, carcinoma biopsy material, and certain epithelia of normal tissues. It immunoprecipitates two components from carcinoma cell lines, a major component of 22 kd which is Oglycosylated and a minor one of 24 kd which is additionally N‐glycosylated. The immunocomplexed 50H.19 antigen exhibits protein kinase activity with substrate‐specificity for casein and phosvitin, but not for histones. It phosphorylates on serine and threonine, but not tyrosine residues. Enzyme activity is cyclic AMP‐independent.