Zhi-Jiang Wang,Wenming Ma,Jun-Mo Yang,Yani Kang,Yong-Doo Park
To gain insight into the effect of Cu 2+ on the activity and structure of alkaline phosphatase (ALP) from Macrobrachium rosenbergii , the enzyme was purified using ammonium sulfate fractionation, Sephacryl S-200, and DEAE anion exchange chromatography . We studied Cu 2+ -mediated inhibition and aggregation of ALP, and found that Cu 2+ significantly inactivated ALP activity with an IC 50 of 1.47 ± 0.02 mM. We further revealed that Cu 2+ reversibly inhibited ALP in a mixed-type manner with K i = 0.41 ± 0.02 mM. Time-interval kinetics showed that the inhibition followed first-order reaction kinetics . This process was associated with conformational changes and significant transient free-energy change. Spectrofluorometry results showed that Cu 2+ induced ALP tertiary structural changes, including the exposure of hydrophobic surfaces that directly induced ALP aggregation. The results provide new information regarding ALP from M. rosenbergii .
In order to investigate the effects of multi-frequency ultrasound-assisted immersion freezing (MUIF) on the meat quality of Macrobrachium rosenbergii , tail meat was subjected to different MUIF treatments respectively, namely 20 + 40 kHz (MUIF-20 + 40), 20 + 60 kHz (MUIF-20 + 60), 40 + 60 kHz (MUIF-40 + 60) and 20 + 40 + 60 kHz (MUIF-20 + 40 + 60), and the immersion freezing (IF) as control. Results showed that average diameter of ice crystals was 28 μm in IF, and that was only 8 μm in MUIF-20 + 40 + 60. When compared to IF, MUIF alleviated oxidative deterioration of lipids and proteins, but only at higher ultrasound frequency (MUIF-40 + 60; MUIF-20 + 40 + 60). Carbonyl content of MUIF-20 + 40 + 60 was only 40% of that in IF. Similarly, protein denaturation was inhibited in MUIF (except for MUIF-20 + 40). Transmission electron microscopy showed greater distortion of the ultrastructural components in IF, MUIF-40 + 60, and MUIF-20 + 40 + 60, suggested by bended Z -line. In conclusion, MUIF can be an effective strategy to mitigate mechanical damage and protein deterioration in the meat of Macrobrachium rosenbergii .
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