JBC, Vol. 252, Issue 6, 1847-1851, Mar, 1977
Properties of immunoreactive glucagon fractions of canine stomach and pancreas
C. B. Srikant, K. McCorkle and R. H. Unger
The present study was designed to identify the physicochemical,
immunologic, and biologic properties of the immunoreactive glucagon (IRG)
moieties of canine gastric fundus and to compare them with those of the
canine pancreas. Acid-alcohol extracts of the gastric fundus and pancreas
of dogs were subjected to Bio-Gel P-10 chromatography, The elution profiles
of extracts of both organs revealed IRG peaks in the Mr = 2,000 3,500, and
9,000 zones; in the gastric extracts, a void volume peak was also present.
On the basis of Sephadex G-150 rechromatography and sucrose density
gradient ultracentrifugation the latter IRG was estimated to have a Mr =
65,000. Incubation of fundic IRG65,000 in 8 M urea failed to alter its
elution position. Its pI was 6.4, while fundic IRG3,500 had a pI of 6.15
and pancreatic glucagon 6.25.Fundic IRG9,000 had a pI of 4.5 and pancreatic
IRG9,000 4.65. Dilution curves of these three fundic and two pancreatic
IRGs were parallel to crystalline beef-pork glucagon. The glycogenolytic
activity of fundic IRG3,500 and IRG65,000, measured in the isolated rat
liver system, was not different from that of immunoequivalent amounts of
dog pancreatic glucagon or crystalline beef-pork glucagon. Both fundic and
pancreatic IRG9,000 were devoid of glycogenolytic activity and lacker
adenylate cyclase stimulating activity and 125I-glucagon displacing
activity when tested on partially purified rat liver membranes. Fundic
IRG65,000, however, stimulated adenylate cyclase and displaced
125I-glucagon to the same degree as immunoequivalent amounts of pancreatic
glucagon. Fundic IRG3,500 was more active than pancreatic glucagon in
stimulating adenylate cyclase activity. This was not clearly attributable
to differences in binding to liver cell membranes.
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