The photosystem II (PSII) manganese-stabilizing protein (PsbO) is known to be the essential PSII extrinsic subunit for stabilization and retention of the Mn and Cl(-) cofactors in the oxygen evolving complex (OEC) of PSII, but its function relative to Ca(2+) is less clear. To obtain a better insight into the relationship, if any, between PsbO and Ca(2+) binding in the OEC, samples with altered PsbO-PSII binding properties were probed for their potential to promote the ability of Ca(2+) to protect the Mn cluster against dark-inhibition by an exogenous artificial reductant, N,N-dimethylhydroxylamine. In the absence of the PsbP and PsbQ extrinsic subunits, Ca(2+) and its surrogates (Sr(2+), Cd(2+)) shield Mn atoms from inhibitory reduction (Kuntzleman et al., Phys Chem Chem Phys 6:4897, 2004). The results presented here show that PsbO exhibits a positive effect on Ca(2+) binding in the OEC by facilitating the ability of the metal to prevent inhibition of activity by the reductant. The data presented here suggest that PsbO may have a role in the formation of the OEC-associated Ca(2+) binding site by promoting the equilibrium between bound and free Ca(2+) that favors the bound metal.

Hydroxide ion inhibits Photosystem II (PSII) activity by extracting Cl(-) from its binding site in the O(2)-evolving complex (OEC) under continuous illumination [Critchley, C., et al. (1982) Biochim. Biophys. Acta 682, 436]. The experiments reported here examine whether two subunits of PsbO, the manganese-stabilizing protein, bound to eukaryotic PSII play a role in protecting the OEC against OH(-) inhibition. The data show that the PSII binding properties of PsbO affect the pH optimum for O(2) evolution activity as well as the Cl(-) affinity of the OEC that decreases with an increasing pH. These results suggest that PsbO functions as a barrier against inhibition of the OEC by OH(-). Through facilitation of efficient retention of Cl(-) in PSII [Popelkova, H., et al. (2008) Biochemistry 47, 12593], PsbO influences the ability of Cl(-) to resist OH(-)-induced release from its site in the OEC. Preventing inhibition by OH(-) allows for normal (short) lifetimes of the S(2) and S(3) states in darkness [Roose, J. L., et al. (2011) Biochemistry 50, 5988] and for maximal steady-state activity by PSII. The data presented here indicate that activation of H(2)O oxidation occurs with a pK(a) of ∼6.5, which could be a function of deprotonation of one or more amino acid residues that reside near the OEC active site on the D1 and CP43 intrinsic subunits of the PSII reaction center.

Review of sociability measurements Boswell et al.

Over the last decade, environmental engineers have developed and applied computerized process simulation models to optimize the design of suspended growth biological wastewater treatment systems. Such models have proven especially useful for designing biological nutrient removal (BNR) plants. The utility of computer simulation depends to a large degree on model calibration, which in turn requires reliable estimates of influent wastewater characteristics as well as the stoichiometric and kinetic constants for each reaction included in the simulator. Unfortunately, reported literature values for several activated sludge model parameters, particularly those related to biological nitrification kinetics, are quite variable. This has led engineers to make conservative assumptions that have resulted in significant overdesign and increased facilities costs.Recognizing these concerns, the Water Environment Research Foundation (WERF) sponsored a project to develop state-of-the-art measurement procedures for activated sludge process model parameters (Melcer et al., 2003). The goal was to provide peer-reviewed methods for process model parameter estimation that would be simple, reproducible, and relatively inexpensive to implement. WERF focused extensively on methods to estimate the maximum specific growth rate (µ AUT ) and endogenous decay rate (b AUT ) of nitrifying bacteria. This paper presents the results of a field application of the WERF low food-to-microorganism (F/M) protocol at Marine Corps Base Camp Pendleton (MCBCP), Oceanside, California. Adjusted to 20 degrees Celsius (ºC), the site-specific estimates for µ AUT obtained during this project were in the range of 0.82 d -1 to 0.84 d -1 , while b AUT was estimated at 0.20 d -1 . These values are comparable to values reported by other researchers at North American domestic sewage treatment plants. This 96-day study demonstrated that reliable nitrification parameter estimates can be obtained using the WERF low F/M protocol, although the procedure is labor intensive and demands significant attention to detail to be executed successfully in a field setting.