Engineering chlorophyll (Chl) pigments that are bound to photosynthetic light-harvesting proteins is one promising strategy to regulate spectral coverage for photon capture and to improve the photosynthetic efficiency of these proteins. Conversion from the bacteriochlorophyll (BChl) skeleton (7,8,17,18-tetrahydroporphyrin) to the Chl skeleton (17,18-dihydroporphyrin) produces the most drastic change of the spectral range of absorption by light-harvesting proteins. We demonstrated in situ selective oxidation of B800 BChl a in light-harvesting protein LH2 from a purple bacterium Rhodoblastus acidophilus by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. The newly formed pigment, 3-acetyl Chl a , interacted with the LH2 polypeptides in the same manner as native B800. B850 BChl a was not oxidized in this reaction. CD spectroscopy indicated that the B850 orientation and the content of the α-helices were unchanged by the B800 oxidation. The nonameric circular arrangement of the oxidized LH2 protein was visualized by AFM; its diameter was almost the same as that of native LH2. The in situ oxidation of B800 BChl a in LH2 protein with no structural change will be useful not only for manipulation of the photofunctional properties of photosynthetic pigment-protein complexes but also for understanding the substitution of BChl to Chl pigments in the evolution from bacterial to oxygenic photosynthesis.

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The deposition of islet amyloid is associated with β-cell mass dysfunction in type 2 diabetes mellitus (T2DM). Since the amylin aggregate is the main component of islet amyloid, in vivo imaging of amylin may be useful for diagnosis and elucidation of the pathogenic mechanism of T2DM. In the present study, we newly designed, synthesized, and evaluated two 18 F labeled compounds ([ 18 F]DANIR-F 2b and [ 18 F]DANIR-F 2c) as positron emission tomography (PET) probes targeting amylin aggregates. In an in vitro binding study, DANIR-F 2b and DANIR-F 2c showed binding affinity for amylin aggregates (K i = 160 and 29 nM, respectively). In addition, [ 18 F]DANIR-F 2b and [ 18 F]DANIR-F 2c clearly labeled islet amyloids in in vitro autoradiography of T2DM pancreatic sections. In the biodistribution study using normal mice, [ 18 F]DANIR-F 2b and [ 18 F]DANIR-F 2c displayed favorable pharamacokinetics in the pancreas and some organs located near the pancreas. Furthermore, in an ex vivo autoradiographic study, [ 18 F]DANIR-F 2c also bound to amylin aggregates in the pancreas of the amylin transplanted mice. The results of this study suggest that [ 18 F]DANIR-F 2c shows fundamental properties as a PET imaging probe targeting amylin aggregates in the T2DM pancreas.