Erratum: Elevated free nitrotyrosine levels, but not protein-bound nitrotyrosine or hydroxyl radicals, throughout amyotrophic lateral sclerosis (ALS)-like disease implicate tyrosine nitration as an aberrant in vivo property of one familial ALS-linked superoxide dismutase 1 mutant (Proceedings of the Nat. Acad. of Sci. of the USA (July 8, 1997) 94:14 (7606-7611))