Fluorescein Labeling Kit-NH2 is mainly used for the preparation of fluorescein-labeled proteins such as IgG for immunostaining and cellular proteins for tracing. Amine-reactive fluorescein, a component of this kit, has succinimidyl groups (NHS) that react with the amino groups on proteins or other molecules (Fig. 1). This kit contains all the reagents necessary for labeling, including storage buffer. Each vial of fluorescein can label up to 200 μg of IgG, conjugating about 4 to 6 fluorescein molecules per IgG molecule. Because this kit also includes a buffer exchange system, a sample containing amine base buffer can be labeled. Although membrane filtration sometimes causes IgG aggregation, the buffer system in this kit prevents aggregation during the concentration of IgG or fluorescein-labeled IgG solution. A fluorescein-labeled IgG solution prepared using this kit is stable for more than 2 months at 4ºC. The excitation and emission wavelengths of the fluoresceinlabeled IgG are 500 nm and 525 nm, respectively (Fig. 2).
Fig. 1 IgG labeling reaction of NH2-reactive fluorescein
Fig. 2 Fluorescence spectrum of fluorescein-conjugated IgG
♦ The molecular weight of the protein to be labeled with this kit should be greater than 50,000.
♦ IgG or fluorescein-conjugated IgG is always on the membrane of the filtration tube during the labeling process.
♦ If the IgG solution contains other proteins with molecular weight greater than 10,000, such as BSA or gelatin, purify the IgG solution before labeling fluorescein with this kit. IgG solution can be purified by IgG Purification Kits (not included in this kit).
♦ If the IgG solution contains small insoluble material, centrifuge the solution and use the supernatant for the labeling.
2) W. Aung, A. Tsuji, H. Sudo, A. Sugyo, T. Furukawa, Y. Ukai, Y. Kurosawa and T. Saga, “Immunotargeting of Integrin α6β4 for Single-Photon Emission Computed Tomography and Near-Infrared Fluorescence Imaging in a Pancreatic Cancer Model”, Molecular Imaging, 2016, 15, 1.
3) A. Shinya, K. Yamamoto, M. Kurata, S. Abe-Suzuki, R. Horii, F. Akiyama and M. Kitagawa, “Targeting MCM2 function as a novel strategy for the treatment of highly malignant breast tumors”, Oncotarget., 2015, 6, (33), 34892.
4) K.M. Nishida, T.N. Okada, T. Kawamura, T. Mituyama, Y. Kawamura, S. Inagaki, H. Huang, D. Chen, T. Kodama, H. Siomi and M.C. Siomi, “Functional involvement of Tudor and dPRMT5 in the piRNA processing pathway in Drosophila germlines”, EMBO J.., 2009, 28, (24), 3820.
5) P.G. Sreekumar, R. Kannan, M. Kitamura, C. Spee, E. Barron, S.J. Ryan and D.R. Hinton, “αB crystallin is apically secreted within exosomes by polarized human retinal pigment epithelium and provides neuroprotection to adjacent cells”, PLoS ONE., 2010, 5, (10), e12578.
6) R. Asano, T. Kumagai, K. Nagai, S. Taki, I. Shimomura, K. Arai, H. Ogata, M. Okada, F. Hayasaka, H. Sanada, T. Nakanishi, T. Karvonen, H. Hayashi, Y. Katayose, M. Unno, T. Kudo, M. Umetsu and I. Kumagai, “Domain order of a bispecific diabody dramatically enhances its antitumor activity beyond structural format conversion: the case of the hEx3 diabody”, Protein Eng. Des. Sel.., 2013, 26, (5), 359.
7) R. Asano, I. Shimomura, S. Konno, A. Ito, Y. Masakari, R. Orimo, S. Taki, K. Arai, H. Ogata, M. Okada, S. Furumoto, M. Onitsuka, T. Omasa, H. Hayashi, Y. Katayose, M. Unno, T. Kudo, M. Umetsu and I. Kumagai, “Rearranging the domain order of a diabody-based IgG-like bispecific antibody enhances its antitumor activity and improves its degradation resistance and pharmacokinetics”, MAbs., 2014, 6, (5), 1243.
8) R. Asano, K. Ikoma, I. Shimomura, S. Taki, T. Nakanishi, M. Umetsu and I. Kumagai, “Cytotoxic enhancement of a bispecific diabody by format conversion to tandem single-chain variable fragment (taFv): the case of the hEx3 diabody”, J. Biol. Chem.., 2011, 286, (3), 1812.
9) T. Toyotome, M. Yamaguchi, A. Iwasaki, A. Watanabe, H. Taguchi, L. Qin, H. Watanabe and K. Kamei, “Fetuin A, a serum component, promotes growth and biofilm formation by Aspergillus fumigatus”, Int. J. Med. Microbiol.., 2012, 302, (2), 108.
10) W. Ma, V. Schubert, M. M. Martis, G. Hause, Z. Liu, Y. Shen, U. Conrad, W. Shi, U. Scholz, S. Taudien, Z. Cheng and A. Houben, “The distribution of α-kleisin during meiosis in the holocentromeric plant Luzula elegans”, Chromosome Res.., 2016, 24, (3), 393.
11) Y. Yokoi, K. Nakamura, T. Yoneda, M. Kikuchi, R. Sugimoto, Y. Shimizu and T. Ayabe, “Paneth cell granule dynamics on secretory responses to bacterial stimuli in enteroids”, Sci. Rep.., 2019, 9, 2710.
12) Y.J. Lee, S.R. Han, N.Y. Kim, S.H. Lee, J.S. Jeong and S.W. Lee, “An RNA aptamer that binds carcinoembryonic antigen inhibits hepatic metastasis of colon cancer cells in mice”, Gastroenterology., 2012, 143, (1), 155.
13) C. F.O.Hoya, K. Kushiro, Y. Yamaoka, A. Ryo and M. Takai, “Rapid multiplex microfiber-based immunoassay for anti-MERS-CoV antibody detection”, Sens Biosensing Res., 2019,10.1016/j.sbsr.2019.100304.