The decay of tyrosine cation radical was found to be biphasic at 253 K. The fast phase corresponds to the YZ* component while the slow phase corresponds to the tyrosine D radical (YD*) component. At 253 K, the t1/2 value was ∼28.6 s for the fast phase and ∼190.7 s for the slow phase. The fast phase is attributed to the recombination of charges between YZ* and QA-. The activation energy for the reaction of YZ with QA- between 253 and 293 K was 48 kJ mol-1 in Cl--depleted photosystem 2 (PS2) membranes. Both the decay rate and the amplitude of the PAR-induced signal of YZ* were affected by addition of chloride anion. Change in the decay rate and the amplitude of the PAR-induced signal of YZ* was observed when other anions like Br-, I-, F, HCO3-, NO3-, PO43- were substituted in the Cl--depleted PS2. and A. Jajoo, S. Bharti, A. Kawamori.
By determining the calcium retention capacity (CRC) of rat liver
mitochondria, we confirmed and extended previous observations
describing the activation of mitochondrial swelling by phosphate
and tert-butyl hydroperoxide (t-BHP). Using CRC measurements,
we showed that both phosphate and t-BHP decrease the extent
of calcium accumulation required for the full mitochondrial
permeability transition pore (MPTP) opening to 35 % of control
values and to only 15 % when both phosphate and t-BHP are
present in the medium. When changes in fluorescence were
evaluated at higher resolution, we observed that in the presence
of cyclosporine A fluorescence values return after each
Ca2+ addition to basal values obtained before the Ca2+ addition.
This indicates that the MPTP remains closed. However, in the
absence of cyclosporine A, the basal fluorescence after each
Ca2+ addition continuously increased. This increase was
potentiated both by phosphate and t-BHP until the moment when
the concentration of intramitochondrial calcium required for the
full opening of the MPTP was reached. We conclude that in the
absence of cyclosporine A, the MPTP is slowly opened after each
Ca2+ addition and that this rate of opening can be modified by
various factors such as the composition of the media and the
experimental protocol used.
A traditional method is reported for purification of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) from leaves of Amaranthus hypochondriacus L. with a high yield of 50 %, 135-fold purification, and specific activity of 900 mmol kg-1(protein) s-1. PEPC was purified from light-adapted leaves of A. hypochondriacus, involving 40-60 % ammonium sulphate fractionation, followed by chromatography on columns of DEAE-Sepharose, hydroxylapatite (HAP), and Seralose 6-B. The enzyme appeared as a single band on 10 % SDS-PAGE, with a molecular mass of about 100 kDa. Kinetic studies with purified enzyme confirmed the PEPC to be the light-form of the enzyme. Glycerol generally increased the stability of PEPC. The stability and storage of the purified enzyme was studied at temperatures of 4 °C, -20 °C, and liquid nitrogen. PEPC maintained its activity for up to 3 months upon storage with 50 % (v/v) glycerol in liquid nitrogen. and J. Gayathri, K. Parvathi, A. S. Raghavendra.