<Li> Phosphorylation of the cytosolic components of NADPH oxidase, a large membrane - bound, multi-protein enzyme present in phagocytic cells, plays an important role in the regulation of protein - protein interactions in the enzyme . </Li> <Li> Important in protein degradation . <Ul> <Li> In the late 1990s, it was recognized that phosphorylation of some proteins causes them to be degraded by the ATP - dependent ubiquitin / proteasome pathway . These target proteins become substrates for particular E3 ubiquitin ligases only when they are phosphorylated . </Li> </Ul> </Li> <Ul> <Li> In the late 1990s, it was recognized that phosphorylation of some proteins causes them to be degraded by the ATP - dependent ubiquitin / proteasome pathway . These target proteins become substrates for particular E3 ubiquitin ligases only when they are phosphorylated . </Li> </Ul> <Li> In the late 1990s, it was recognized that phosphorylation of some proteins causes them to be degraded by the ATP - dependent ubiquitin / proteasome pathway . These target proteins become substrates for particular E3 ubiquitin ligases only when they are phosphorylated . </Li>

Which of the following groups of amino acids can be phosphorylated