Studies on limited proteolysis of 6-phosphofructo-1-kinase (Pfk-1) from Saccharomyces cerevisiae led to the suggestion that the C-terminal part of the alpha-subunit must contribute to the stabilisation of the octameric enzyme structure. To analyse the role of the C-terminus in vivo. the respective terminus of one of both types Of Subunits of Pfk-1 was sequentially truncated or extended. These modifications resulted in a decrease of the protein level of the mutated subunit and of the specific enzyme activity in the cell-free extract as ell as in changes of the kinetic properties. Size exclusion HPLC demonstrated that the modified subunit is still able to assemble with the native counterpart generating an enzymatically active hetero-octamer. On the basis of our results we assume that the C-termini are important for the three-dimensional structure of the subunits determining their susceptibility to proteolysis and the ability assembly to an active. oligomeric Pfk-1. (C) 2002 Elsevier Science (USA). All rights reserved.