Phosphorylation of bovine neurofilament proteins by protein kinase FA (glycogen synthase kinase 3).
A highly purified preparation of protein kinase FA (where FA is the activating factor for phosphatase 1)/glycogen synthase kinase 3 from rabbit muscle readily phosphorylated bovine neurofilaments. All three neurofilament proteins, the high, middle, and low molecular proteins (NF-H, NF-M, and NF-L), were phosphorylated when intact filaments were incubated with the kinase. Experiments with individual proteins showed that NF-M was the best substrate. At protein concentrations of 0.13 mg/ml, the initial rate of NF-M phosphorylation was 30% of that observed for glycogen synthase. Km values were 0.24 mg/ml (7 x 10(-7) M tetramer) for glycogen synthase and 0.10 mg/ml (5 x 10(-7) M dimer) for NF-M. Vmax values were 0.36 mumol/min/mg for glycogen synthase and 0.035 mumol/min/mg for NF-M. Dephosphorylated NF-M was phosphorylated only half as much as native NF-M; this is consistent with the known substrate specificity of the kinase. The possible involvement of FA/GSK-3 in the phosphorylation of neurofilaments in vivo is discussed.
Guan
R J
RJ
Department of Chemistry and Biochemistry, California State University, Long Beach 90840.
Khatra
B S
BS
Cohlberg
J A
JA
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002417:Cattle; D038341:Glycogen Synthase Kinases; D007381:Intermediate Filament Proteins / Q000378:metabolism*; D007700:Kinetics; D016900:Neurofilament Proteins; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits
D007381:Intermediate Filament Proteins; D016900:Neurofilament Proteins; D011494:Protein Kinases; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases