The phrase "phosphorylation level" refers to the number of phosphate molecules added to a specific molecule in a cell. It basically indicates how many phosphates are attached to that particular molecule. Full definition
(H) Spleen CD4 + T cells harvested from VPA recipients and control mice on day 21 were analyzed by Western blot assay for the expression and phosphorylation level of Akt and downstream target proteins. (jimmunol.org)
Laboratory measurements of receptor phosphorylation levels — which indicate the level of their activity — showed that, in fact, deactivation rates were roughly the same for both the internal and surface receptors. (pnnl.gov)
The team then performed the validation laboratory tests to determine the actual EGFR phosphorylation levels in cells, both for all the cell receptors and for only the internal receptors. (pnnl.gov)