Anthony A. Donchev

Learn More
The stability of the two isoforms of poplar plastocyanin (PCa and PCb) was studied with differential scanning calorimetry (DSC) technique. It was shown that the thermal unfolding of both isoforms is an irreversible process with two endothermic and one exothermic peaks. The melting temperature of PCb was found to be 1.3+/-0.2 K degrees higher than of PCa,(More)
Two total plastocyanin (PC) fractions - loosely bound (lPC) and strongly bound (sPC) were extracted (84% and 16%, respectively) from the homogenate of Scenedesmus acutus MT8. Two-fold isolation-purification procedure including DE-52 chromatography separated IPC into a smaller oxidized [IPC (II)] and a larger reduced [IPC(I)] fractions, in contrast to sPC,(More)
Using gas–mass chromatography analyses (GS-MS) we have determined the endogenous levels of jasmonic acid (JA) in developing sunflower seeds. The level of JA was higher in the early phases of seed development. We have registered a maximum on day 5 after pollination. Spraying of plants with JA at the time of flowering induced marked changes in protein(More)
An improved four-stage isolation and purification procedure for preparing poplar isoplastocyanins is described in detail. Absorbance (UV-VIS) spectroscopy and isoelectric focusing (IEF) are used to determine the protein purity and identity. The present procedure increases twice the total plastocyanin (PC) yield. Four PC isoform fractions are consecutively(More)
A detailed study of the tyrosine spectral characteristics was carried out in a broad range of pHs for both isoforms of plastocyanin from poplar. It was found that Tyr 80 is always protonated while Tyr 83 can form a tirosinate at high pHs. The pK(a) of Tyr 83 is practically identical in plastocyanin a and b, but the quenching of its spectrum is different in(More)
Plastocyanin (PC) from poplar leaves is present in two isoforms, PCa and PCb, which differ in sequence by amino acid replacements at locations remote from the copper center and simultaneously act in the photosynthetic electron-transport chain. We describe ultra-high resolution structures of PCa and high-resolution structures of PCb, both under oxidizing and(More)
The redox potentials of poplar plastocyanins a and b (PCa, PCb) were determined by spectrophotometric titrations of their reduced forms with [Fe(CN)6]3-. It was found that the two isoforms have the following millimolar extinction coefficients epsilon597 equilibrium constants Keq of one-electron exchange with [Fe(CN)6]4-/[Fe(CN)6]3-, and standard electron(More)
AIMS To evaluate the lytic activities of crude enzymes from Cytophaga sp. LR2 on Rhodella reticulata cells and isolated algal polysaccharide. METHODS AND RESULTS The Cytophaga compartment was separated after centrifugation in a cell suspension for 30 min at 18,000 g. The extracellular enzyme was obtained from the supernatant and the intracellular from the(More)
Two iso-plastocyanin fractions, oxidized b-plastocyanin, PCb(II) and reduced a-plastocyanin, PCa(I), have been isolated from whole tobacco leaves by conventional chromatography on DEAE-cellulose. The isoelectric points of PCa and PCb at 10 degrees C were found to be 3.99 and 3.97, respectively. When the primary structures were analysed, a microheterogeneity(More)
Changes in the content of isoplastocyanins a (PCa) and b (PCb) in Populus nigra leaves were studied during complete vegetation cycle (from April 30 to October 28). Measurements were made every 7 days. The procedure included extraction and purification of total protein followed by analytical isoelectric focusing and densitometry of obtained isophoregrams.(More)