Polyamine Binding Sites in the Rat Brain Hippocampus Plasma Membranes: MK 801 Does Not Influence the Binding Process

Abstract

The study was undertaken to characterize the polyamine binding sites in rat brain hippocampus plasma membranes. There were two types of binding sites for putrescine, B_max 650 and 100 pmol/mg protein, with K_d1 = 39.2 and K_d2 = 6.7 µM, respectively, while those for spermidine (Spd) and spermine (Spm) represented only one type of population with B_max 2.55 and 15 nmol/mg protein, respectively. The K_d values for Spd and Spm were 34 and 30.3 µM, respectively. The maximum binding of polyamines was found at pH 8.0. The binding capacity of these molecules was curtailed at 4°C, indicating that the binding is an energy-dependent phenomenon. The specific binding was not appreciably influenced by the addition of MK 801, an antagonist of NMDA receptor, indicating that there are polyamine-specific binding sites that are different from those for MK 801. Glycine also did not significantly influence the binding of these biogenic amines. Interestingly, the addition of polyamino acids (polylysine, polyornithine, and polyglutamic acid) inhibited the polyamine binding to their receptor sites, supporting the notion that positive charge of polyamines could be important factor in the binding process.

Key Words:

• Spermidine
• putrescine
• spermine
• polyamino acids