post-transiationaI modification of a protein either through the cross-linking of polypeptide chains via the diamine cross-link or by alteration of the charge of the protein when only one amine group

Measurement of the content of polyamines in pancreatic i s le t s i nd ica t ed tha t no significant change in their c o n c e n t r a t i o n took p lace during g lucose-s t imula ted insulin release. The finding~ together with the absence of any e f fec t of c~-difluoromethylornithine on glucosestimulated insulin release suggested that rapid synthesis of po lyamines is not involved in stimulus-secretion coupling in the B-cell. The concentration of polyamines found in islets were high enough for them to act as substrates for the Ca2+-dependent islet transglutaminase during insulin release. This was further demonstrated by the ability of islet transglutaminase to incorporate [ l~C]pu t r e sc ine into proteins from islet homogenates and by the demonstration of an increase in the covalent incorporat ion of [14C]putrescine into the proteins of i n t a c t is Jets fol lowing their challenge with glucose. Unlike monoamine s u b s t r a t e s of t r a n s g l u t a m i n a s % putrescine failed to ef fec t ively inhibit insulin release when its intracellular concentration was increased. A role for polyamines in the secretory process through their incorporation into islet proteins is suggested.