Characterization of photosystem II assembly complexes containing ONE-HELIX PROTEIN1 in Arabidopsis thaliana.

The assembly process of photosystem II (PSII) requires several auxiliary proteins to form assembly intermediates. In plants, early assembly intermediates comprise D1 and D2 subunits of PSII together with a few auxiliary proteins including at least ONE-HELIX PROTEIN1 (OHP1), OHP2, and HIGH-CHLOROPHYLL FLUORESCENCE 244 (HCF244) proteins. Herein, we report the basic characterization of the assembling intermediates, which we purified from Arabidopsis transgenic plants overexpressing a tagged OHP1 protein and named the OHP1 complexes. We analyzed two major forms of OHP1 complexes by mass spectrometry, which revealed that the complexes consist of OHP1, OHP2, and HCF244 in addition to the PSII subunits D1, D2, and cytochrome b559. Analysis of chlorophyll fluorescence showed that a major form of the complex binds chlorophyll a and carotenoids and performs quenching with a time constant of 420 ps. To identify the localization of the auxiliary proteins, we solubilized thylakoid membranes using a digitonin derivative, glycodiosgenin, and separated them into three fractions by ultracentrifugation, and detected these proteins in the loose pellet containing the stroma lamellae and the grana margins together with two chlorophyll biosynthesis enzymes. The results indicated that chlorophyll biosynthesis and assembly may take place in the same compartments of thylakoid membranes. Inducible suppression of the OHP2 mRNA substantially decreased the OHP2 protein in mature Arabidopsis leaves without a significant reduction in the maximum quantum yield of PSII under low-light conditions, but it compromised the yields under high-light conditions. This implies that the auxiliary protein is required for acclimation to high-light conditions.

Mechanism of Suppression of Blood Glucose Level by Calcium Alginate in Rats.

Calcium alginate (Ca-Alg) is known to suppress the postprandial increase of blood glucose, and therefore may be helpful for preventing lifestyle-related diseases such as diabetes. In this work, we examined the mechanism of this effect. As α-amylase activity and α-glucosidase activity are involved in the digestion of starch, we examined the in vitro inhibitory effect of Ca-Alg on these enzymes. Ca-Alg showed little inhibition of α-amylase, but markedly inhibited α-glucosidase activity. The direct binding affinity of glucose for Ca-Alg was low. Also, Ca-Alg had essentially no effect on the membrane permeability of glucose. Therefore, we considered that the suppression of blood glucose by Ca-Alg is predominantly due to a decrease in the efficiency of starch digestion as a result of inhibition of α-glucosidase, possibly due to increased viscosity of the gastrointestinal contents. Next, we investigated the optimum amount in the diet and the optimum particle size of Ca-Alg for suppressing postprandial blood glucose level in rats orally administered a diet containing starch with various amounts and particle sizes of Ca-Alg. We found that 5% by weight of 270-mesh-pass Ca-Alg was most effective.