Carboxypeptidase H in bovine pituitary gland: soluble forms are not processed at the C-terminus

Carboxypeptidase H (CP-H) has been characterized in anterior and posterior lobes of bovine pituitary with regard to subcellular distribution, enzymatic properties, nature of membrane association, number of forms and C-terminal processing. Anterior lobe contained both soluble and membrane forms of CP-H with similar enzymatic properties after extraction at pH 5.5. The soluble forms represented about 70% of the total activity. Two soluble and two membrane forms, of 53 and 56 kDa, were demonstrated by immunoblotting and after purification. The amount of the 56 kDa soluble form increased with the salt content of the extraction buffer. Endoglycosidase digestions showed that the difference in size was not due to differential N-linked glycosylation and also showed that CP-H oligosaccharides do not become resistant to endoglycosidase H. CP-H in posterior lobe was also composed from about 70% soluble and 30% membrane forms. Only 53 kDa CP-H was detected in soluble and membrane fractions of posterior lobe. All forms of CP-H from both lobes reacted with antiserum directed to the C-terminus. These results do not support previous observations that soluble and membrane forms of CP-H can be distinguished by size and C-terminal processing.