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J. Biochem, 1996, Vol. 119, No. 4 783-790
© 1996 Japanese Biochemical Society

research-article

Two Phosphorylations Specific to the Tail Region of the 204-kDa Heavy Chain Isoform of Porcine Aorta Smooth Muscle Myosin1

Yasuhiro Fukui and Fumi Morita2

Division of Chemistry, Graduate School of Science; Hokkaido University Sapporo, Hokkaido 060

2 To whom correspondence should be addressed.

In a porcine aorta extract, we observed two protein kinase activities which specifically phosphorylate the 204-kDa heavy chain isoform of aorta myosin in the absence of conventional kinase activators. We referred to these two protein kinases, eluted at 0.15 and 0.2 M KC1 from a DEAE-column, as myosin kinases I (MKI) and II (MKII), respectively. The phosphorylation site for MKI was determined using a purified phosphopeptide derived from porcine aorta myosin phosphorylated with MKI. By comparison with the deduced amino acid sequence for smooth muscle myosins, the site corresponded to a Ser located at 3 amino acids upstream from a Pro, the putative end of the a-helical segment of the 204-kDa heavy chain tail. A homologous Ser is only present in smooth muscle myosins, i.e. not in nonmuscle myosins. MKI was purified 130-fold, but not separated from a kinase activity phosphorylating Serl or Ser2 in the 20-kDa regulatory light chain of aorta myosin. In contrast, MKII was purified to near homogeneity. MKII phosphorylated the porcine aorta myosin heavy chain at a Ser 19 amino acids downstream from the MKI site. The amino acid sequence around the Ser shared a consensus sequence of the phosphorylation site for casein kinase II and was homologous to that reported for bovine aorta myosin [Kelley, C.A. and Adelstein, R.S. (1990) J. Biol. Chem. 265, 17876–17882]. MKII was identified as a multifunctional protein kinase, casein kinase II.

1 This work was supported in part by a Special Grant-in-Aid for the Promotion of Education and Science in Hokkaido University, and by a Grant-in-Aid for General Scientific Research from the Ministry of Education, Science and Culture. A part of this work was performed at the Research Center for Molecular Genetics of Hokkaido University.


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