Inhibitory activities of baicalin against renin and angiotensin-converting enzyme.

CONTEXT: Baicalin has been characterized as the active compound and quality control marker in Scutellaria baicalensis Georgi, traditionally used as a hypotensive herb. OBJECTIVES: To investigate the inhibitory activities of baicalin against renin and angiotensin-I converting enzyme (ACE) and their molecule mechanism of interactions. METHODS: The fluorescence method using renin substrate 1(R-2932) and the spectroscopy method by Cushman were used to determine renin and ACE activities, respectively. The fluorescence quench techniques were used to characterize their interactions. RESULTS: The results showed that baicalin inhibited renin activity with an IC(50) value of 120.36 µM and inhibited ACE activity with an IC(50) value of 2.24 mM in vitro. The fluorescence emission of both renin and ACE were efficiently quenched by baicalin and a complete quenching was achieved at a high concentration of baicalin. Furthermore, baicalin was more effective in quenching the fluorescence of renin (K(SV) = 60 × 10(3) M(-1)) than ACE (K(SV) = 17.1 × 10(3) M(-1)). The quenching of fluorescence of renin and ACE involved static interactions, which was characterized by the formation of quencher-enzyme complex. The baicalin-renin complex formed through three-sites binding including the active site with a binding constant of 796.15 × 10(13) M(-1), but there was only one binding site for the baicalin-ACE complex with a much smaller binding constant of 6.8 × 10(5) M(-1). CONCLUSION: The inhibition activity of baicalin against renin was a result of the formation of stable complex through multisites binding including the active site, which could explain the higher inhibitory efficiency.

Physicochemical and bitterness properties of enzymatic pea protein hydrolysates.

The effects of different proteolytic treatments on the physiochemical and bitterness properties of pea protein hydrolysates were investigated. A commercial pea protein isolate was digested using each of 5 different proteases to produce protein hydrolysates with varying properties. After 4 h of enzyme digestion, samples were clarified by centrifugation followed by desalting of the supernatant with a 1000 Da membrane; the retentates were then freeze-dried. Alcalase and Flavourzymetrade mark produced protein hydrolysates with significantly higher (P < 0.05) degree of hydrolysis when compared to the other proteases. Flavourzyme, papain, and alcalase produced hydrolysates that contained the highest levels of aromatic amino acids, while trypsin hydrolysate had the highest levels of lysine and arginine. Papain hydrolysate contained high molecular weight peptides (10 to 178 kDa) while hydrolysates from the other 4 proteases contained predominantly low molecular weight peptides (

Some physicochemical and functional properties of cowpea (Vigna unguiculata) isoelectric protein isolate as a function of pH and salt concentration.

Cowpea isoelectric protein isolate was prepared by alkali extraction followed by acid precipitation at pH 4.5. Physicochemical and functional properties of the isolate were determined at various combinations of pH (3-8) and NaCl concentrations (0.5-2.0 M). Results showed that at all NaCl concentrations, emulsifying activity index, heat coagulability, aromatic hydrophobicity (ARH) and fluorescence intensity (FI) were high at low pH and gradually decreased with increasing pH. Protein solubility and foam stability were low at low pH and high NaCl concentrations, but increased with increase in pH. The relationships of ARH, FI and UV-absorption maxima (Amax) with the functional properties were determined using multiple regression analyses. Significant (P < or = 0.05) equations describing the functional properties on the basis of ARH, FI and Amax were generated; however, the contribution of these parameters was low as indicated by the low correlation coefficients. Regression results suggest that other physicochemical properties (e.g. electrostatic interactions) were also important contributors to the functional properties examined.