A sterile solution of amino acids and peptides prepared from a protein by acid or enzymatic hydrolysis and used intravenously for the maintenance of positive nitrogen balance in severe illness, after surgery of the alimentary tract, in the diets of infants allergic to milk, or as a high protein dietary supplement. Protein hydrolysates have a range of applications in the food and allied healthcare sectors. Bitterness is a negative attribute associated with most food protein hydrolysate.

To track protein expression, localization, or conformational changes as components of cellular signaling pathways, biologists need general tools for the in vivo site-specific labeling of proteins with fluorophores or other useful probes. Fluorescein and its derivatives have been the most popular fluorescent derivatization reagents for covalently labeling proteins because of their relatively high absorptivities, excellent fluorescence quantum yields and high water solubilities. In addition, fluorescein-protein conjugates are usually not susceptible to precipitation. Fluorescein has an excitation maximum that closely matches the 488 nm spectral line of the argon ion laser, making it the predominant fluorophore for confocal laser scanning microscopy and flow cytometry applications. Many widespread optical filter sets are designed to excite efficiently and detect fluorescein's fluorescence. Fluorescein can most commonly be introduced into a protein through in vitro modifications with suitable amine-reactive reagents, such as N-hydroxysuccinimidylfluorescein.

The term 'nutrient sensing' has been defined and interpreted in different ways. In the narrowest sense, a nutrient sensor is a protein whose binding to a nutrient leads to a change inthe function of that protein, which in some cases may triggerdownstream activation of a signalling cascade. Nutrients suchas AAs (amino acids), glucose and fatty acids have traditionallybeen considered as metabolic fuels for cell growthand development. But this view is undergoing a rapid changewith an increased understanding of the mechanisms bywhich such nutrients can act as mediators of signal transductionpathways. These nutrient-mediated signalling cascades regulate specific aspects of fuel and energy metabolism,ultimately influencing cell growth, proliferation and survival.