This investigation of the temperature dependence of DppA interactions with a subset of three dipeptides (AA. AF and FA) by isothermal titration calorimetry has revealed the negative heat capacity ([Formula: see text]) that is a characteristic of hydrophobic interactions. The observation of enthalpy-entropy compensation is interpreted in terms of the increased structuring of water molecules trapped in a hydrophobic environment, the enthalpic energy gain from which is automatically countered by the entropy decrease associated with consequent loss of water structure flexibility. Specificity for dipeptides stems from appropriate spacing of designated DppA aspartate and arginine residues for electrostatic interaction with the terminal amino and carboxyl groups of a dipeptide, after which the binding pocket closes to become completely isolated from the aqueous environment. Any differences in chemical reactivity of the dipeptide sidechains are thereby modulated by their occurrence in a hydrophobic environment where changes in the structural state of entrapped water molecules give rise to the phenomenon of enthalpy-entropy compensation. The consequent minimization of differences in the value of ΔG0 for all DppA-dipeptide interactions thus provides thermodynamic insight into the biological role of DppA as a transporter of all dipeptides across the periplasmic membrane.
An aqueous extraction of moringa (Moringa oleifera) leaves were prepared as the edible coats for keeping the quality of the giant freshwater prawn (Macrobrachium rosenbergii). In addition, the antioxidant properties and activity; total phenolic content (TPC), total flavonoid contents (TFC), free radical scavenging activity (DPPH), and ferric reducing antioxidant power (FRAP) of moringa leaves were also determined. The phenolic compounds and antioxidant properties in the moringa leaves are low; 16.14 mgGAEg-1 for TPC; 5.57 mgQEg-1 for TFC; 1.36 mgTEg-1 for DPPH; and 3.05 mgTEg-1 for FRAP. The experiment was further conducted by coating the M. rosenbergii with moringa leaves extraction before chilled storage at 4°C for 15 days. Moringa leaves extraction were effectively reduced the microflora count in M. rosenbergii (P<0.05). Total volatile basis nitrogen (TVB-N) value showed a significant (P<0.05) lower amount in treated samples compared to the controls. Melanosis were obvious in controls compared to the treated samples. After 15 days of chilled storage, the sensory properties; taste, texture and odour of treated samples were acceptable by the panelists. Biopreservation of moringa leaves extraction significantly benefits in keeping the quality of M. rosenbergii.