Source:http://linkedlifedata.com/resource/umls/id/C0031689
CSP: protein phosphorylation is probably the most ubiquitous and diverse molecular mechanism of biological signal transduction; thus many proteins (not all treed here) may be phosphorylated at some time.,NCI: Proteins that contain phosphate groups esterified to serine, threonine or tyrosine. The phosphate group usually regulates protein function. (On-line Medical Dictionary)