Characterization of polyamine transport systems and modulation of NMDA receptor by polyamines

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1.Cycling of polyamines (spermine and spermidine) in the brain was examined by measuring polyamine transport in synaptic vesicles, synaptosomes and glial cells, and the release of spermine from hippocampal slices. Membrane potential-dependent polyamine transport systems exist in synaptosomes and glial cells, and a proton gradient-dependent polyamine transport system exists in synaptic vesicles. Spermine was found to be accumulated in synaptic vesicles and was released from rat hippocampal slices by depeolarization. Polyamines may function as neuromodulators in the brain.2.Extracellular protons inhibit NMDA receptors. To identify the molecular determinants of proton sensitivity, we used scanning mutagenesis of NR1 subunit. The majority of mutations that affected proton sensitivity were clustered in the extracellular end of the second transmembrane domain and adjacent linker leading to the S2 portion of the glycine binding domain of NR1. The proton sensor and receptor gate may be structu … More rally and functionally integrated.3.The ATPase activity of PotA, a component of the spermidine-preferential uptake system consisting of PotA, B, C, and D, was studied using purified PotA and a PotABC complex. When PotA was associated with PotB and PotC, PotA became more sensitive to inhibition by spermidine, suggesting that spermidine functions as a feedback inhibitor. The NH_2-terminal domain contains the ATP binding pocket andt he active center of ATPase. The COON-terminal domain of PotA contains a site that regulates ATPase activity and a site involved in the spermidine inhibition of ATPase activity.4.The functions of cadaverine transport protein CadB were studied in Escherichia colt: CadB had both cadaverine uptake and cadaverine excretion activities. At acidic pH, the operon containing cadB and cadA, encoding lysine decarboxylase, was induced in the presence of lysine, leading to generation of a proton motive force. The cadBA operon plays important roles in cellular regulation at acidic pH. Less