3′,5′-cyclic AMP binds to and promotes polymerisation on platelet tubulin

Abstract

IN spite of considerable research, the regulatory mechanism of the reversible assembly–disassembly of microtubules remains obscure. Of the various processes and agents which have been examined as potential regulators probably none has received as much attention as cyclic nucleotides. Indeed, the number of reports which indicate that adenosine 3′,5′-cyclic monophosphate (cyclic AMP) exerts a stimulatory effect in the formation of microtubules, or maintains the latter in the presence of dissociative influences is steadily growing^1–13. Most of these studies used intact cells, however, leaving unclear whether the cyclic nucleotide was directly or indirectly involved in this process. To try to resolve this problem, I have used tubulin extracted from platelets: addition of exogenous cyclic AMP has been reported to prevent cold-induced disassembly of microtubules in about 50% of the platelets¹⁴. I show here that cyclic AMP stimulates the assembly of microtubules and binds to platelet tubulin, primarily to the α-subunit.