Secretion of high and low molecular weight phosphorylated apolipoprotein B by hepatocytes from control and diabetic rats. Phosphorylation of APO BH and APO BL.
Apolipoprotein B (apo B) phosphorylation was examined in primary cultures of hepatocytes from control and nonketotic streptozotocin diabetic rats. Following a 5-h incubation with ortho[32P]phosphate, media lipoproteins (d less than 1.063 g/ml) were isolated, and delipidated apolipoproteins were separated by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis (SDS-PAGGE), and gels were heat fixed. Autoradiographic bands corresponding to high (apo BH) and low molecular weight apo B (apo BL) were observed in media lipoproteins isolated from control rats, and these bands were more prominent in media lipoproteins isolated from diabetic rats. Apo B-specific activity was estimated from aqueous alcohol-precipitated radioactivity and apo B monoclonal immunoassay of isolated media lipoproteins. In lipoproteins secreted by hepatocytes of diabetic rats, the calculated apo B specific activity was between 18- and 31-fold greater than that secreted by hepatocytes of control rats, consistent with the SDS-PAGGE gel data. The increase in secretory 32P-labeled apo B from hepatocytes of diabetic rats was due, at least in part, to an increase in labeled phospho-tyrosine as determined by phosphoamino acid analysis. These data demonstrate that apo BH may be secreted as a phosphorylated protein and that apo B phosphorylation occurs on tyrosine as well as serine residues.
D000818:Animals; D001055:Apolipoproteins B / Q000378:metabolism*; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D008099:Liver / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D019000:Phosphotyrosine; D051381:Rats; D011919:Rats, Inbred Strains; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D001055:Apolipoproteins B; D010768:Phosphoserine; D019000:Phosphotyrosine; D014443:Tyrosine