What is the function of tyrosine-kinase receptors?
A. enzymatic degrading of GTP to GDP
B. enzymatic phosphorylation of tyrosine in the receptor protein
C. enzymatic hydrolyzing of the signaling molecule shortly after its arrival
D. allowing specific ions to enter the cell after ligand binding
E. binding to nonpolar signaling molecules such as nitric oxide or the steroid hormones
Answer: B