Catalytic and physical features of a naturally immobilized Yarrowia lipolytica lipase in cell debris (LipImDebri) displaying high thermostability.

Abstract

Lipase activity (337U/g dry weight of cell debris) was detected in cell debris after ultrasound treatment of Yarrowia lipolytica cells cultivated in residual frying palm oil. It is a naturally immobilized lipase with protein content of 47%, herein called LipImDebri. This immobilized biocatalyst presents low hydrophobicity (8%), that can be increased adjusting pH and buffer type. Despite apparent intact cells, electron microscopy showed a shapeless and flat surface for LipImDebri and optical microscopy revealed no cell viability. Besides, an inferior mean diameter (3.4mm) in relation to whole cells reveals structure modification. A high negative zeta potential value (-33.86mV) for pH 6 and 25°C suggests that LipImDebri is a stable suspension in aqueous solution. Fourier Transform Infrared Spectra (FTIR) expose differences between LipImDebri and extracellular lipase extract signaling a physical interaction between enzyme and cell debris, which is possibly the reason for the high thermostability (k d = 0.246h-1; t 1/2 = 2.82h at 50°C, pH 7.0). A good adjustment of LipImDebri kinetic data with Hill equation (R 2 = 0.95) exposes an allosteric behavior related to the presence of more than one lipase isoform. These features reveal that LipImDebri can be a good catalyst for industrial applications.