Inter-domain interaction of ferredoxin-NADP+ reductase important for the negative cooperativity by ferredoxin and NADP(H).

Ferredoxin-NADP+ reductase (FNR) in plants receives electrons from ferredoxin (Fd) and converts NADP+ to NADPH. The affinity between FNR and Fd is weakened by the allosteric binding of NADP(H) on FNR, which is considered as a part of negative cooperativity. We have been investigating the molecular mechanism of this phenomenon and proposed that the NADP(H)-binding signal is transferred to the Fd-binding region across the two domains of FNR, NADP(H)-binding domain and FAD-binding domain. In this study, we analyzed the effect of altering the inter-domain interaction of FNR on the negative cooperativity. Four site-directed FNR mutants at the inter-domain region were prepared, and their NADPH-dependent changes in the Km for Fd and physical binding ability to Fd were investigated. Two mutants, in which an inter-domain hydrogen bond was changed to a disulfide bond (FNR D52C/S208C) and an inter-domain salt bridge was lost (FNR D104N), were shown to suppress the negative cooperativity by using kinetic analysis and Fd-affinity chromatography. These results showed that the inter-domain interaction of FNR is important for the negative cooperativity, suggesting that the allosteric NADP(H)-binding signal is transferred to Fd-binging region by conformational changes involving inter-domain interactions of FNR.

Chronic diverticulitis of the large intestine characterized by stenosis symptoms in Japan: report of 6 cases.

The concept of chronic diverticulitis, which is characterized by stenosis symptoms, has recently been proposed. However, it is not widely known in Japan. To stress the prevalence of this disease in Japan, we herein report 6 patients with chronic diverticulitis who required surgery. The present study involved both clinicopathological analyses of 6 patients and a review of case reports in Japan. The site involved in all 6 patients was the left-sided colon. Stenosis symptoms (i.e., ileus) were observed in all 6 patients. Preoperative clinical diagnoses were diverticulitis (n = 4) and suspected type 4 colon cancer (n = 2). Histopathological examination confirmed the presence of diverticulitis and fibrous thickening of the bowel wall due to chronic diverticulitis in all patients. Our review of the case reports of 32 patients with chronic diverticulitis in Japan revealed that the site most frequently involved was the left-sided colon, despite the fact that diverticulitis occurs most frequently in the right-sided colon in Japan. The present report confirmed that chronic diverticulitis is not an uncommon disease, with the same preponderance in the left-sided colon also in Japan. Therefore, we need to bear in mind the concept of chronic diverticulitis for patients with colonic obstruction.