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Umikinoko-Green Fluorescent Protein

  • Bright green fluorescence
  • High pH stability
  • Useful for FRET
  • Labeling of proteins and subcellular structures

The fluorescent protein Umikinoko-Green (UkG) gene was isolated from the soft coral Sarcophyton sp. (umi-kinoko in Japanese).

UkG rapidly matures to form a dimeric complex. CoralHue® monomeric Umikinoko-Green (mUkG1) maintains the brightness and pH stability of parent protein UkG. mUkG1 absorbs light maximally at 483 nm and emits green light at 499 nm. mUkG1 exhibits brilliant fluorescence and has extremely high pH stability. mUkG1 can be used to label proteins, subcellular structures or for FRET analysis.

Performance and use

Voltage sensor “Mermaid”

Mermaid is a membrane potential reporter using FRET. The structure of Mermaid consisting of the VSD of Ci-VSP and mUkG1-mKOκ in tandem. mUKG1 and mKO-κ are good FRET partners of donor and acceptor. mUKG’s emission and mKO-κ’s absorption greatly overlapped with a calculated Förster distance of 5.5 nm.


  1. Tsutsui H, Karasawa S, Okamura Y, Miyawaki A. Improving membrane voltage measurements using FRET with new fluorescent proteins.; Nat Methods., 5, 683-685(2008) PMID: 18622396 Within this paper, the use of Umikinoko-Green for FRET analysis is described.

Fluorescent properties

Umikinoko-Green spectrum data files (text files)

Note: The file is in a tab-delimited text format. It contains values of the wavelength (0.5nm spacing) and brightness (fluorescence intensity peak value normalized to 1). Use a spreadsheet program to create a spectrum that will help you in choosing the appropriate excitation filter, dichroic mirror and fluorescence filter.

Characteristic mUkG1
Oligomerization monomer
Number of amino acid 227
Excit./Emiss. Maxima (nm) 483/499
Molar extinction coefficient (M-1cm-1) 60,000 (483 nm)
Fluorescence quantum yield 0.72
Brightness*1 43.2
pH sensitivity pKa=5.2
Cytotoxicity*2 No

*1Brightness: Molar Extinction Coefficient x Fluorescence Quantum Yield / 1000
*2Toxicity when expressed in HeLa cells