Sequential hydration of dry proteins: A direct difference IR investigation of sequence homologs lysozyme and α‐lactalbumin

Abstract

SynopsisDirect difference ir spectra are presented as a function of hydration for lysozyme and u-lactalbumin, and detailed sequential hydration molecular events identified. Despite the strong sequence homology between the two proteins, and their expected conformational similarity, the hydration behavior of the polar groups is different for the two proteins. Using a Hill-type analysis, we conclude that the acid groups ionize and hydrate rapidly and noncooperatively in both proteins, consistent with the known (lysozyme) and postulated (a-lactalbumin) surface chemistry. The polar group hydration shows a clear cooperativity, which is quantitatively different in the two proteins. Complementary work suggests this cooperativity relates to a hydration-induced "loosening up" of the lysozyme conformation a t about 55 mol water/mol protein. u-Lactalbumin appears to "open up" more easily for hydration than does lysozyme, consistent with its lower stability against thermal and acid denaturation.

The Different Molar Absorptivities of the Secondary Structure Types in the Amide I Region: An Attenuated Total Reflection Infrared Study on Globular Proteins

“…Also, the band intensity is known to correlative small contribution of b-turns present in proteins might contribute to this. The small uncertainty relate positively with the transition dipole moment (44), as demonstrated for a series of ketones (45). The in the parameter obtained for the random coil can be the basis of their intensity at specific positions in amide I, our findings demonstrate that changes in b-stranded or a-helical regions are easily overestimated, whereas those of b-turns or random coiled parts might be undersuggestion that the strength of H-bonding within a secondary structure type (b-strand ú a-helix ú b-turn ú estimated.…”

Rapid Non-destructive Detection of Spoilage of Intact Chicken Breast Muscle Using Near-infrared and Fourier Transform Mid-infrared Spectroscopy and Multivariate Statistics

“…Interestingly, this correlation shows that there is a simultaneous increase in both signals that could be interpreted as a direct increase of free amino acids and peptides as the period of storage lengthens; as proteins get digested, they fold into random structures and smaller α helices and β pleated sheets that hydrogen bond with water and other molecules present at the muscle surface. This strengthening of the interaction with water molecules has been reported to increase the absorption of the amide I band (Byler and Susi 1986;Poole and Finney 1984) and possibly explain this phenomenon, but direct evidence on meat muscle decomposition does not exist. On the other hand, the increase of free amino acids and peptides as a result of proteolysis has been reported in studies performed in chicken breast muscle, broiler carcasses and beef muscle spoilage (Nychas and Tassou 1997;Pittard et al 1982;Adams and Moss 2000;Sams 2001).…”

“…It is generally accepted that spoilage of chicken breast fillets under aerobic conditions becomes readily detectable when the total viable count (TVC) reaches 8 log 10 cfu g −1 (Nychas and Tassou 1997;Gill and Newton 1978;Ellis et al 2002) and is mainly due to the presence of microorganisms such as Pseudomonas spp., lactic acid bacteria and B. thermosphacta (Nychas and Tassou 1997); the relative contribution of these to the final mix of flora is reported to depend on the packaging methods utilised (Brown 1982). Metabolic by-products of these microorganisms are responsible for the spoilage odour of chicken breast muscle (Poole and Finney 1984). When population levels have reached 8 log 10 cfu g −1 , it is believed that microorganisms switch from the diminishing levels of glucose to amino acids as a growth substrate (Nychas and Tassou 1997).…”

Structural Relaxation During Drying and Rehydration of Food Materials—the Water Effect and the Origin of Hysteresis

“…Previous work by infrared spectroscopy, suggests that at these low moisture levels, even charged groups become dehydrated, and this would lead to high electrostatic association forces in proteins 40 . However, in uncharged polysaccharides, the same form of hysteresis is observed, implying that weaker intermolecular hydrogen bonding may be adequate to produce the same effect.…”