Which of the following describes a characteristic feature of fluorophores like GFP?

Fluorophores like Green Fluorescent Protein (GFP) are known for their ability to exhibit bright fluorescence when exposed to specific wavelengths of light, a property that is crucial for their use in various biological applications, including imaging and tracking in living cells. This bright fluorescence arises because the protein has chromophores that undergo electronic transitions when excited, leading to the emission of light, which is typically at a longer wavelength than that of the absorbed light. This characteristic is essential for their effectiveness as markers in biological research, allowing scientists to visualize and study cellular processes in real time.

In contrast, other options do not align with the properties of GFP. For instance, GFP is actually water-soluble, which allows it to be used in aqueous environments such as living cells. It is also functional at a variety of temperatures, not limited to high temperatures, and does not require heavy metal ions for its fluorescence to occur. These features underline the versatility and utility of GFP as a tool in molecular and cellular biology.