Open AccessMetabolism of Insulin and Glucagon
Author(s) -
Ansorge Siegfried,
Bohley Peter,
Kirschke Heidrun,
Langner Jürgen,
Hanson Horst
Publication year - 1971
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1971.tb01316.x
Subject(s) - glucagon , insulin , cytosol , microsome , hormone , biochemistry , metabolism , medicine , endocrinology , chemistry , intracellular , centrifugation , enzyme , biology
Using radioiodinated ( 131 I or 125 I) hormones, the intracellular localization of enzyme systems involved in the degradation of insulin and glucagon was studied in rat liver. The breakdown of I‐labelled hormones was followed by measuring the increase of trichloroacetic acid soluble radioactivity during incubations of cell fractions with radioiodinated hormones at neutral and and acidic pH.1 Glucagon was degraded at pH 7 mainly by the cytosol fraction, with or without addition of GSH and EDTA. 2 Without effectors the insulin breakdown took place predominantly in the cytosol fraction at pH 7. 3 However, using 1 mM GSH and 5 mM EDTA the distribution pattern of insulin breakdown at pH 7 was completely different; under these conditions about 90% of insulin degrading activities were located in the microsomal fraction and only about 10% in the cytosol fraction. 4 In contrast to glucose‐6‐phosphatase the insulin‐degrading activities were soluble after deoxycholate treatment of microsomes; by subsequent centrifugation at 2 × g for some hours the insulin‐degrading activities in the supernatant were purified about 10‐ to 24‐fold (as compared with the homogenate). The specific activity of this supernatant was about 20–48 times higher than that of the cytosol fraction. 5 At acidic pH both glucagon and insulin were degraded predominantly by the lysosomal fractions of rat liver.