Tyrosine confounds oxidative electrochemical detection of nitric oxide.

We report evidence that a porphyrinic microsensor for detection of nitric oxide (NO) also detects biologically relevant concentrations of tyrosine (Tyr) in dog brain. Tyr is oxidized by this sensor at the same potential as NO, and the sensitivity for NO and Tyr are of the same order of magnitude. The interference from Tyr is of importance because 1) Tyr is abundant and 2) there is a concentration gradient of Tyr across the blood-brain barrier that can lead to unpredictable results if disturbed by ischemia or hypoxia. The knowledge of this interference is important for the interpretation of results obtained with this sensor and for the design of future studies.