The nature of the phosphorus linkage in component I, a phosphoprotein isolated from the blood serum of DES-treated cockerels.

The nature of the phosphorus linkage in electrophoretic component I of the blood serum of DES-treated cockerels was investigated by enzymatic and partial acid and alkali dephosphorylation. The C-P bond was excluded because this bond is stable to 6 N HCl at 110 degrees C. for 20 hours, and all the phosphorus was released under these conditions. No phosphorus was released when diesterase, pyrophosphatase and 0.25 N HCl were employed, and this excludes the diester, pyrophosphate and N-P bonds. The presence of the O-P bond was supported by the release of phosphate by the phosphatases and 0.25 N NaOH. The hydrolysate produced upon hydrolysis with pronase and papain contained phosphoserine. No phosphothreonine was present.