Activation of Mg-ATPase of skeletal-muscle myosin by bovine retinal pigment epithelial actin.
The morphology and function of actin in cultured bovine retinal pigment epithelial (RPE) cells were studied. Filamentous actin was identified with a fluorescent mushroom toxin, nitrobenzoxadiazole (NBD)-phallacidin, specific for actin. Dark-field microscopy of cultured RPE cells revealed numerous pigment granules; fluorescent microscopy identified scattered lipofuscin granules. One-dimensional SDS polyacrylamide gel electrophoresis of urea-soluble proteins extracted from RPE cells showed a 46,000-dalton protein band which comigrated with authentic muscle actin. Densitometric scanning showed that this protein band comprised 7.6% of the total urea-soluble proteins. An actin-activated skeletal-muscle myosin Mg-ATPase assay, using skeletal-muscle heavy meromyosin as enzyme and [gamma-32P]-ATP as substrate, demonstrated functional actin in RPE cell extracts after DEAE-cellulose anion exchange chromatography. The actin-containing protein fractions were eluted at ionic strengths between 0.19 and 0.36 M KCl. The activation of myosin ATPase by actin in RPE cells provides a molecular basis for the phagocytic activity which is important in maintaining the integrity of retinal photoreceptor cells.
Chan
L S
LS
Department of Ophthalmology, Scheie Eye Institute, School of Medicine, University of Pennsylvania, Philadelphia.
Khatami
M
M
Li
W Y
WY
Rockey
J H
JH
D000199:Actins / Q000032:analysis* / Q000502:physiology; D000546:Amanitins; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005456:Fluorescent Dyes; D009132:Muscles / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000032:analysis* / Q000502:physiology
D000199:Actins; D000546:Amanitins; D005456:Fluorescent Dyes; C028877:7-nitrobenz-2-oxa-1,3-diazole-phallacidin; D009218:Myosins