Journal of Clinical Endocrinology & Metabolism, Vol 40, 393-400, Copyright © 1975 by Endocrine Society
Chromatographic heterogeneity of insulin extracted from insulomas
W Beischer, F Melani, L Keller and EF Pfeiffer
On gel filtration of acid-ethanol extracts from three pancreatic beta- cell
adenomas 1.4% to 1.8% of total immunomeasurable insulin (IMI) eluted ahead
of proinsulin. This high molecular IMI was resolved into three components.
The presence of urea in the dilute acetic acid solutions of extracted tumor
tissue did not influence the pattern of gel filtration. High molecular IMI
dissolved in dilute acetic acid showed to be stable if immediately
rechromatographed, but a partial dissociation to insulinlike and
proinsulinlike components (ILC and PLC) was found if rechromatography was
performed after 48 h of incubation. Mainly ILC and PLC were found on
rechromatography provided high molecular IMI was dissolved and incubated
briefly in 0.04M phosphate buffer, pH 7.4. It proved improbable that the
proteolytic action of some protein being extracted with the hormones caused
a splitting of high molecular IMI at pH 7.4. We conclude from our findings
that the components of high molecular IMI are not precursors of proinsulin
and insulin but are either self-associated products of the hormones or
associations of insulin and proinsulin to other proteins extracted from
insuloma tissue.
