POLYAMINE CONTENT AND SPERMINE TRANSPORT IN RAT-BRAIN MITOCHONDRIA

It is shown that spermidine and spermine are present in rat brain mito chondria at concentration of 1.7 and 2.1 nmoles/mg mitochondrial prote in respectively. Evidence is also provided that brain mitochondria are capable to take up spermine in a process strictly dependent on a high transmembrane potential. This can be induced by energizing mitochondr ia with succinate plus rotenone, in the presence of 1 mM Pi. Under the se conditions a membrane potential of 150 mV is achieved and spermine is taken up in a saturable process with an apparent Km of 0.12 mM and a Vmax of 0.67 nmol min(-1) * mg(-1). Spermine uptake is non competi tively inhibited by the presence of Mg2+ in the suspending medium (Ki = 1.1 mM). Spermine transport increases sharply and non ohmically with membrane potential. The dependence on membrane potential indicates th at spermine, like Ca2+, crosses the membrane electrophoretically. Howe ver the uptake of this polyamine, unlike that of Ca2+, is a very slow process and it is unaffected by ruthenium red indicating that spermine transport should occur on a different uniporter.