Which amino acid is one that is targeted for phosphorylation to modulate the activity of an enzyme?

Explanation:

Serine threonine, tyrosine in eukaryotes and also histidine in prokaryotes and plants are the most typically phosphorylated amino acids (though it is now known to be common in humans). These phosphorylations have crucial and well defined functions in the pathways of signalling and metabolism.

Phosphorylation is the most frequent process of protein function regulation and cellular signal transmission. While phosphorylation in bacterial proteins has been seen, in eukaryotic cells it is far more prevalent.

plasma is the state of matter where the substance is ionized and has no definite shape or volume. the fact of being ionized makes the substance a good electrical conductor.