Overlapping distribution of the 130- and 110-kDa myosin I isoforms on rat liver membranes.
The biochemical and mechanochemical properties and localization of myosin I suggest the involvement of these small members of the myosin superfamily in some aspects of intracellular motility in higher cells. We have determined by quantitative immunoblotting with isoform-specific antibodies that the 130-kDa myosin I (myr 1 gene product) and 110-kDa myosin I (myr 2 gene product) account for 0.5 and 0.4%, respectively, of total rat liver protein. Immunoblot analyses reveal that the 130- and 110-kDa myosins I are found in several purified subcellular fractions from rat liver. The membrane-associated 130-kDa myosin I is found at the highest concentration in the plasma membrane (28 ng/microg plasma membrane protein) followed by the endoplasmic reticulum-like mitochondria-associated membrane fraction (MAM; 10 ng/microg MAM protein), whereas the 110-kDa myosin I is found at the highest concentration in Golgi (50 ng/¿g Golgi protein) followed by plasma membrane (20 ng/microg) and MAM (7 ng/microg). Our analyses indicate that myosin I is peripherally associated with Golgi and MAM and its presence in these fractions is not a consequence of myosin I bound to contaminating actin filaments. Although found in relatively low concentrations in microsomes, because of the abundance of microsomes, in liver most of the membrane-associated myosin I is associated with microsomes. Neither myosin I isoform is detected in purified mitochondria. This is the first quantitative analysis addressing the cellular distribution of these mammalian class I myosins.
Balish
M F
MF
Boston Biomedical Research Institute, Massachusetts 02114, USA.
Moeller
E F
EF
Coluccio
L M
LM
D000818:Animals; D002462:Cell Membrane / Q000737:chemistry; D003599:Cytoskeleton / Q000737:chemistry; D007425:Intracellular Membranes / Q000737:chemistry; D008099:Liver / Q000737:chemistry*; D008297:Male; D008930:Mitochondria, Liver / Q000737:chemistry; D008970:Molecular Weight; D009218:Myosins / Q000032:analysis* / Q000737:chemistry; D020033:Protein Isoforms / Q000032:analysis / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000737:chemistry
D020033:Protein Isoforms; D009218:Myosins