Conformational and Structural Changes of Choline Oxidase from Alcaligenes Species by Changing pH Values

Abstract

Results of intrinsic and extrinsic fluorescence studies on choline oxidase revealed that the enzyme at high alkaline pH values has more accessible hydrophobic patches relative to acidic pH. Fluorescence quenching studies with acrylamide confirm these changes. The quenching constants were also determined at different pH(s) by using the Stern-Volmer equation. CD studies showed that at higher pH a transition from α-helix to β-structure was appeared while at lower pH the content of α-helix structure was increased. Furthermore, analysis of the spectral data using chemometric method gave evidence for existence of intermediate components at very high pH(s). Results of thermal denaturation evaluated that the enzyme has the most instability at higher pH(s). Altogether low and high pH values caused significant alteration on secondary and tertiary structures of choline oxidase via inducing of an intermediate.

Phase Behavior of Internal Mixtures of Hydrocarbon-like Primary Organic Aerosol and Secondary Aerosol Based on Their Differences in Oxygen-to-Carbon Ratios

“…From these images, the morphology (see Section S3) and the number of phases in the POA + SOA particles can be determined. The number of phases can be determined because the fluorescence spectrum of Nile red, a solvatochromic dye, is different (different emission wavelength and hence different color) when embedded in the different types of chemical phases. , The color depends on the polarity of the surrounding phase, , as well as to some degree on experimental conditions, including the water content in the particles, , the pH of the organic phase, the aggregation of the solvatochromic dye, , and the fluorescent detector settings. In our experiments, the POA-dominated phase appeared mostly green for POA with a low O/C ratio and yellow to orange for POA with a higher O/C ratio.…”