Two-dimensional total shift correlation spectroscopy (TOCSY) and double-quantum-filtered phase-sensitive homonuclear shift-correlated spectroscopy (DQF-COSY) H-1 NMR spectra are used to assign peaks for about one sixth of the amino acids residues of isolated human serum albumin (67 kDa) to amino acid types. Sequential assignments are presented for H-1 NMR resonances of the N-terminal residues Asp1, Ala2 and His3 of human serum albumin (HSA). These are based on pH-dependent chemical shifts reflecting the titrating N-terminal NH2 and the His3 imidazole ring, in addition to DQF-COSY and TOCSY experiments. Studies of variant recombinant human albumin with Asp1 deleted, rHA(2-585), aided the assignments. The structural nature of the N-and C-termini of HSA are discussed and pK(a) values of 7.9 and 6.3 were determined for the N-terminal amino group and His3 imidazole ring, respectively. About 20 spin systems for albumin, including those for the N-terminal amino acids, were assigned in H-1 NMR spectra of blood plasma by comparison with isolated albumin. Resonances fbr lipids within lipoproteins and also several low molecular mass components can also be assigned in 2D TOCSY H-1 NMR spectra of plasma.
