ABSTRACT
Copper (Cu) plays a key role in the photosynthetic process as cofactor of the plastocyanin (PC), an essential component of the chloroplast photosynthetic electron transfer chain. Encoded by the nuclear genome, PC is translocated in its apo-form into the chloroplast and the lumen of thylakoids where it is processed to its mature form and acquires Cu. In Arabidopsis, Cu delivery into the thylakoids involves two transporters of the PIB-1 ATPases family, heavy metal associated protein 6 (HMA6) located at the chloroplast envelope and HMA8 at the thylakoid membrane. To gain further insight into the way Cu is delivered to PC, we analysed the enzymatic properties of HMA8 and compared them with HMA6 ones using in vitro phosphorylation assays and phenotypic tests in yeast. These experiments reveal that HMA6 and HMA8 display different enzymatic properties: HMA8 has a higher apparent affinity for Cu(+) but a slower dephosphorylation kinetics than HMA6. Modelling experiments suggest that these differences could be explained by the electrostatic properties of the Cu(+) releasing cavities of the two transporters and/or by the different nature of their cognate Cu(+) acceptors (metallochaperone/PC).
Subject(s)
Adenosine Triphosphatases/metabolism , Arabidopsis Proteins/chemistry , Arabidopsis Proteins/metabolism , Copper/metabolism , Adenosine Triphosphatases/genetics , Adenosine Triphosphate/metabolism , Arabidopsis Proteins/genetics , Chloroplast Proton-Translocating ATPases/metabolism , Copper/pharmacology , Lactococcus/genetics , Molecular Docking Simulation , Phosphorylation , Plastocyanin/chemistry , Plastocyanin/metabolism , Protein Conformation , Saccharomyces cerevisiae/drug effects , Saccharomyces cerevisiae/genetics , Thylakoids/metabolismABSTRACT
N-Butyl-phosphorotriamide (NBPT) is a fertilizer widely used for its urease inhibiting properties. Nevertheless, formulations currently commercialized are complex and do not avoid severe decrease of activity due to the low stability of the bioactive compound under acidic conditions. According to its structure, NPBT was thought to be able to interact with both polar additives, by its phosphoramide function, and hydrophobic ones, through its alkyl chain. In this context, and in order to simplify formulations of this bioactive compound, a panel of natural polysaccharides was studied, including starch, ß-(1,3)-glucans, carraghenans and alginates. We also used cyclodextrins, characterized the most stable inclusion complex with α-cyclodextrin and evaluated the stability of NBPT thus protected against hydrolysis under acidic conditions.
