Available Lysine in Protein, Assay Using o‐Phthalaldehyde/ N‐Acetyl‐L‐cysteine Spectrophotometric Method

Abstract

An assay was based on reaction of free c-amino groups in proteins with the o-phthalaldehydefi-ace@-L-cysteine reagent to form isoindoles, which absorb at 335 nm. The procedure was suitable for proteins or mixtures of proteins with available lysine contents of more than 5 moles lysine/mole protein and required absence of free amino acids and peptides. This method was simpler and more convenient than other methods, since it did not require hydrolysis, amino acid analysis, long heating periods or solvent extraction.

Loss of filament‐forming ability of myosin by non‐enzymatic glycosylation and its molecular mechanism

“…The solubility of the protein was expressed as a percent of the protein concentration in the supernatant with respect to that of the protein solution before centrifugation. Assays of available lysine [17] and fructosamine [18] were carried out to evaluate the progress of the non‐enzymatic glycosylation between the protein and the reducing sugars. Before available lysine analysis, glycosylated proteins were precipitated with 7.5% TCA and redissolved in 2% SDS solution to remove unreacted sugars [11].…”

Antioxidative Ability of Chicken Myofibrillar Protein Developed by Glycosylation and Changes in the Solubility and Thermal Stability

“…We then examined the thermal stability and SOSA in glycosylated myofibrillar proteins after 24-and 36-h reactions by using an ESR analysis, since it is known that some intermediate products of the Maillard reaction possess active oxygen scavenging properties. [20][21][22][23] Thermal stability Unglycosylated myofibrillar protein and samples glycosylated with 4 times the amount of maltose after 24-and 36-h reaction were respectively dissolved in 0.1 and 0.5 M NaCl solutions (pH 7.5) and then heated at 50 C for 2 h. Figure 7 shows the solubility of the glycosylated and unglycosylated myofibrillar protein samples before and after heating. The solubility of the unglycosylated sample in 0.5 M NaCl was significantly decreased from about 65% to 13% (Fig.…”

Cooperative effect of relative humidity and glucose concentration on improved solubility of shellfish muscle protein by the Maillard reaction

“…After removal of TCA by decantation, the precipitated protein was redissolved in 50 mM phosphate buffer (pH 9.5) containing 2% sodium dodecylsulfate (SDS). The available lysine content was determined by spectrophotometric analysis using o ‐phthalaldehyde and N ‐acetyl‐L‐cysteine 18 . The available lysine content of Mf before reaction with glucose was 0.097 g/g protein.…”