| Abstract |
It is known that glucagon is synthesized via a large precursor molecule
and that conversion of the precursor to glucagon is accomplished by
selective proteolytic cleavage of proglucagon. lmmuno-reactive glucagons
(IRGs) with various molecular weights were obtained from acid-ethanol
extracts of glucagon-producing tumor cells (ITC-1) in Syrian golden
hamster by gelfiltration on Bio-Gel P-30 and CNBr-activated Sepharose 4B.
The biological activity of various IRGs in vitro was examined by measuring
the release of cAMP from the isolated hamster liver cells. Liver cells
were isolated from adult Syrian hamsters by the method of Seglen. The
cells were preincubated in RPMI-1640 medium for 5 hours. The release of
cAMP into the culture medium was deterrnined by radioimmunoassay.
Cyclic AMP accumulation in the medium containing porcine crystalline
glucagon was observed. At addition of 10-ii moles it was 0.73 pmole/10^6
cells/h, while at addition of 10^-8 moles it was 4.14 pmole/10^6 cells/h.
Extracted IRGs from the tumor also had elevated cAMP concentration. (In
the case of IRG3500, at addition of 2.4 x 10^-10 moles it was 2.67
pmole/10^6 cells/h, while with addition of 7.5 x 10^-10 moles it was 16.7
pmole/10^6 cells/h. ln the case of IRG9000, and addition of 0.7 x 10^-10
moles it was 0.7 pmole/10^6 cells/h, while with addition of 2.9 x 10 ^-10
moles it was 0.93 pmole/10^6 cells/h).
A similar tendency in the result of intracellular cAMP and the results
obtained from the medium. Glucagon from extracted ITC-1 tumor has
biological activity causing a quantity of glucagon release from liver
cells of hamsters, cAMP component in liver cells. The release of cAMP from
liver cells was low in animals with tumors compared with control animals.
These results suggested that the biological activity of extracted tumor
glucagon was highest in glucagon with a molecular weight of 3500. IRG of
molecular weight 3500 showed biological activity similar to that of
standard glucagon.
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