J. Biol. Chem., Vol. 265, Issue 17, 9701-9706, Jun, 1990
Developmental regulation of glucosidase I, an enzyme involved in the processing of asparagine-linked glycoproteins in rat mammary gland
K Shailubhai, ES Saxena, AK Balapure and IK Vijay
Department of Animal Sciences, University of Maryland, College Park 20742.
Glucosidase I involved in the processing of N-linked glycoproteins was
purified to homogeneity from the lactating rat mammary gland. The purified
enzyme exhibited a single band at 85 kDa on 10% sodium dodecyl
sulfate-polyacrylamide gel electrophoresis under reducing conditions.
Polyclonal antibodies raised against the enzyme recognized a similar band
on Western blots and also inhibited the enzyme activity. The enzyme levels
gradually increased until the midlactation stage and thereafter declined
sharply during the period of postlactation. A similar profile of the levels
of immunoreactive glucosidase I was observed. These findings suggest that
the accumulation of glucosidase I is modulated as a function of gland
ontogeny. The results on hormonal regulation of glucosidase I indicate that
the synthesis of the enzyme is stimulated by a combination of insulin,
hydrocortisone, and prolactin; additionally, epidermal growth factor may
play a role in this regulation. The above observation was substantiated by
immunoprecipitation of [35S]methionine-labeled microsomal extracts with
anti-glucosidase I antibodies. The immunoprecipitation of soluble extracts
from [35S]methionine-labeled tissue with anti-rat alpha- lactalbumin
antibodies indicates that these hormones not only stimulate the synthesis
of alpha-lactalbumin but also play an important role in its glycosylation.