Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction?
A) tyrosines
B) glycine and histidine
C) serine and threonine
D) glycine and glutamic acid
E) Any of the 20 amino acids are equally phosphorylated.

Question

Quizplus · Accepted Answer

Serine and threonine are the amino acids most frequently phosphorylated by protein kinases in the cytoplasm. Tyrosines are also commonly phosphorylated, but not as frequently as serine and threonine. Glycine and histidine are not commonly phosphorylated by protein kinases, and glycine and glutamic acid are not known to be phosphorylated at all by protein kinases. Therefore, choice C is the best answer.

Which of the Following Amino Acids Are Most Frequently Phosphorylated