Recent evidence indicates that the NO-related species, nitroxyl anion (NO-), is produced in physiological systems by several redox metal- containing proteins, including hemoglobin, nitric oxide synthase (NOS), superoxide dismutase, and S-nitrosothiols (SNOs), which have recently been identified in brain. However, the chemical biology of NO- remains largely unknown. Here, we show that NO- - unlike NO-, but reminiscent of NO+ transfer (or S-nitrosylation) - reacts mainly with Cys-399 in the NR2A subunit of the N-methyl-D-aspartate (NMDA) receptor to curtail excessive CA2+ influx and thus provide neuroprotection from excitotoxic insults. This effect of NO- closely resembles that of NOS, which also downregulates NMDA receptor activity under similar conditions in culture.
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