Plant Protein Extraction and Identification from Eurycoma longifolia by Gel Electrophoresis and Mass Spectrometry

Plant protein is seldom studied by researchers, particularly from the roots of Eurycoma longifolia. This is mainly due to the minute amount of plant protein and low sample recovery of protein extraction from the recalcitrant tissues. However, plant protein could be the bioactive constituent for numerous biological activities which have been proven scientifically and practicing traditionally. Therefore, four extraction methods ranging from simple maceration (water extraction without and with detergent, Triton X-100) to buffer-assisted precipitation approaches (phenol-SDS and TCA-acetone) were carried out to extract plant protein from the roots of E. longifolia harvested from Pahang and Perak, Malaysia. The results showed that water extraction produced lower yield (0.1% w/w), but higher protein content (13-29 mg/g pellet) than precipitation methods. The higher protein content in water extraction method also produced higher number of protein spots (5-6), and better resolution of the polyacrylamide gel image. The mass peptide fragments revealed that mostly mitochondrial proteins were detected due to the plant cell lysis by the non-ionic detergent, Triton X-100. On the other hand, hydrophobic proteins with higher molecular size (46-51 kDa) were only found in the phenol-SDS and TCA-acetone precipitation methods. The findings conclude that different extraction methods produced different kinds of plant proteins.