Studies on latent and soluble polyphenol oxidase from Moringa oleifera Lam. leaves

Polyphenol oxidase (PPO) from Moringa oleifera leaves was investigated to unravel its unique properties that can be exploited for possible biotechnological application(s). Soluble and latent PPO were extracted and purified to homogeneity using a combination of three-phase partitioning and gel filtration chromatography. The purity and molecular weight of the purified protein were estimated by SDS-PAGE and further by nano liquid chromatography-electrospray ionization tandem mass spectrometry (Nano-LC-ESI-MS/MS) and amino acid composition determination. Physicochemical and kinetic properties of the purified Moringa oleifera PPO (moPPO) were investigated following established protocols. Two soluble isoforms and a latent form of PPO were purified from the leaves of Moringa oleifera. All purified proteins were monomeric with molecular weights ranging from 10 to 65 kDa. PPO with the lowest molecular weight was further confirmed to be 7.6 kDa, 10.5 ± 0.06 kDa 7.2 kDa, and 8.61 ± 1.69 kDa as estimated by Nano-LC-ESI-MS/MS, SDS-PAGE, amino acid composition determination, and SEC respectively. The soluble proteins have pH optima at pH 6.5 and slightly basic pH 8.0, and that of the latent PPO was found to be 5.5 and 8.0 respectively. The optimal temperature for the purified enzymes was between 15 ᵒC – 25ᵒC and their catalytic efficiency was between 0.4 - 1.9 x 105 M−1s−1. The study concluded that M. oleifera leaves contain at least three forms of PPO, a novel low molecular weight peptide enzyme, a soluble form and a latent form with high kcat/Km similar to those obtainable from other sources which could be of interest in biotechnological applications. [Display omitted] •Moringa oleifera polyphenol oxidase was purified using a new approach.•A peptide enzyme was purified and its molecular weight was estimated using four different techniques.•The kinetics and physicochemical properties of the purified enzymes were investigated.•The overall results suggest that M. oleifera PPOs is suitability of in various biotechnological uses.