Abstract: Peptidic molecules suitable for three dimensional NMR structure determination are provided which have been substituted with .sup.13 C and/or .sup.15 N in the backbone and/or at the .alpha.-carbon with .sup.2 H but not otherwise in the sidechains of the amino acid residues. One or more amino acids, amino acid species or substantially all of the amino acid residues of the molecule may be so substituted. A method of making the substituted peptidic molecules substituted in this manner is provided.

Abstract: A method for determining three-dimensional structural information of a protein which involves producing the protein in a form substantially labeled with .sup.13 C of .sup.15 N or both substantially labeled with .sup.15 N and .sup.13 C and partially labeled with .sup.2 H and subjecting the protein to nuclear magnetic resonance spectroscopic analysis. The isotopically labeled protein is produced by a method which involves producing a substantially labeled microbial protein hydrolysate, subjecting the protein hydrolysate to cation exchange chromatography to produce a partially purified labeled amino acid mixture, subjecting the partially purified labeled amino acid mixture to anion exchange chromatography to produce a purified labeled amino mixture and supplementing the purified labeled amino acid mixture with isotopically labeled cysteine and optionally with isotopically labeled glutamine and asparagine.