N-F Transition

Rudolph, R., Holler, E. and Jaenicke, R. 1975. Fluorescence and stop-flow studies on N-F transition of serum albumin. Biophys. Chem. 3, 226-233. 

Sogami, M. 1971. Effect of salts on the N-F transition of bovine serum plasma albumin. J. Biochem. 69, 819-822. 

Sogami, M. and Foster, J. F. 1968. Isomerization reactions of charcoal-defatted hovine plasma albumin. The N-F transition and acid expansion. Biochemistry 7, 2172-2182. 

The ultraviolet absorption spectra of cysteine, cystine, and methionine are shown in Figs. 2, 3, and 11. The lowest energy (long-wave absorption band) transitions have been assigned (Mulliken, 1935 Walsh, 1953) as n — (f transitions. Transition assignments for disulfide spectra have been critically discussed in a recent paper by McGlynn et al. (1962). The... 

Serum albumin exists in a compact form between pH 4.3 and 10.5 but undergoes conformational expansions below pH 4.3 and above pH 10.5 (Tanford et al., 955a,b Yang and Foster, 1954 Bro et al., 1955 Weber, 1952). Conformational transitions not accompanied by molecular expansion also occur, nhmely the N-F transition between pH 4.8 and 3.9 and the neutral transition, N-B, observed between pH 7 and 9 (Leonard etal., 1963). 

Human serum albumin (HSA) is very similar to BSA in physical properties (Foster, 1960) and also in the N-F transition near pH 4 (Clark et al., 1962). Therefore, most of the information discussed in Sections I and II will also pertain to HSA. The amino acid sequence of HSA has recently been established (Behrens et al., 1975 Meloun et al., 1975) and shows that the three-domain feature that prevailed in BSA is also evident in the structure of HSA (Fig. 23). However, there were some differences between the data of the two groups. Sequences reported by Meloun et al (1975) included phenylalanine at position 157, which was deleted in the original sequence of Behrens et al. (1975). However, the latter group (Behrens, private communication, 1977) included a phenylalanine at position 157. Other differences occurred in the assignment of acid/amide states of the acidic amino acids and also in the identity of residues at 16 positions. 

Pronounced minima of interfacial tension at pH = 3 (Fig. 6) may reflect the isomerization reaction of albumin and the presence of a Fast isomeric form (F). It can be seen (Fig. 6), in agreement with other authors 16,38 that N-F transition is sensitive to the salt concentration in the bulk solution. Once again similar influence of the apolar air phase, in our case, and of a hydrophobic polyethylene on albumin adsorption at this pH is demonstrated. 

The given sequence indicates that protonation of the COO groups and microenvironmental changes in the side chains predominantly precede the secondary stmctural change of a-helix, followed by those of )5-strand and / -turn. It is, thus, likely that the protonation of some carboxylic groups at relatively low pH (4.5-5.0) is triggering the secondary structural changes (i.e., N-F transition) in domain III. 

---