ヨウ素酸イオンと亜硫酸水素イオンによる時計反応における自触媒作用の研究

(1) IO_3^-とHSO_4^-とによる時計反応は, 両イオン濃度について各一次反応たることを実験上見出した。(2) 実験は小量化および簡単に定量できるよう工夫して液滴を用いて行なった。高価薬品, 空気にふれずに, 回数多く繰り返えして行なう場合に特に有効と思われる。(3) 質量作用の法則を用いて濃い原溶液の方が誘導期が短かい事実を説明することに矛盾があることを指摘した。(4) 実験上H^+の濃度で反応速度に増減あることを見出し, HSO_3^-が酸化されH^++SO_4^となるために生成するH^+の自触媒作用と考えた。したがってIO_3^-とHSO_3^-との濃度積による, 反応形式上は二次反応を示すが Mechanism としては生成するH^+の濃度の増加に基づく一次反応によるとすることによって実験結果の説明ができることを明らかにした。本報告に当っては理学博士伊藤良一氏の有益なご助言を得たので, ここに謝意を表する

A Class III Semaphorin (Sema3e) Inhibits Mouse Osteoblast Migration and Decreases Osteoclast Formation In Vitro

Originally identified as axonal guidance cues, semaphorins are expressed throughout many different tissues and regulate numerous non-neuronal processes. We demonstrate that most class III semaphorins are expressed in mouse osteoblasts and are differentially regulated by cell growth and differentiation: Sema3d expression is increased and Sema3e expression decreased during proliferation in culture, while expression of Sema3a is unaffected by cell density but increases in cultures of mineralizing osteoblasts. Expression of Sema3a, -3e, and -3d is also differentially regulated by osteogenic stimuli; inhibition of GSK3β decreased expression of Sema3a and -3e, while 1,25-(OH)2D3 increased expression of Sema3e. Parathyroid hormone had no effect on expression of Sema3a, -3b, or -3d. Osteoblasts, macrophages, and osteoclasts express the Sema3e receptor PlexinD1, suggesting an autocrine and paracrine role for Sema3e. No effects of recombinant Sema3e on osteoblast proliferation, differentiation, or mineralization were observed; but Sema3e did inhibit the migration of osteoblasts in a wound-healing assay. The formation of multinucleated, tartrate-resistant acid phosphatase–positive osteoclasts was decreased by 81% in cultures of mouse bone marrow macrophages incubated with 200 ng/mL Sema3e. Correspondingly, decreased expression of osteoclast markers (Itgb3, Acp5, Cd51, Nfatc1, CalcR, and Ctsk) was observed by qPCR in macrophage cultures differentiated in the presence of Sema3e. Our results demonstrate that class III semaphorins are expressed by osteoblasts and differentially regulated by differentiation, mineralization, and osteogenic stimuli. Sema3e is a novel inhibitor of osteoclast formation in vitro and may play a role in maintaining local bone homeostasis, potentially acting as a coupling factor between osteoclasts and osteoblasts