Quantitation of inhibitory G-proteins in fat cells of obese and normal-weight human subjects.
Antisera were raised in rabbits against synthetic peptides corresponding to sequences of the guanine nucleotide binding proteins Gi1, Gi2, Gi3 and Go. These and previously described antisera were used to identify different G-proteins in Western blots of human adipocyte plasma membranes and to quantify them using purified recombinant alpha subunits as standards. Go was shown to be absent or << 15 pmol/mg of protein. A band stained by a previously characterized Go antiserum is suggested to be due to nonspecific staining of Gi1. Gi1 and Gi2 were the major G-proteins. Gi1 was present at concentrations of 52 and 18 pmol/mg of protein in lean and obese subjects, respectively, and the concentration was negatively correlated with the body mass index. Gi2 concentrations averaged 64 pmol/mg of protein and there was no correlation to the body mass index. Gi3 levels were much lower (<< 13 pmol/mg of protein) and the presence of this protein could not be demonstrated with certainty. The concentrations of Gi1 and Gi2 are thus over two orders of magnitude higher than those of the receptors whose effects they mediate. The low concentration of Gi1 in adipocyte plasma membranes of obese subjects could in part explain the attenuated inhibitory responses of adenylate cyclase in isolated fat cells in obesity.
Kaartinen
J M
JM
Department of Medical Chemistry, University of Helsinki, Finland.
LaNoue
K F
KF
Ohisalo
J J
JJ
D017667:Adipocytes / Q000378:metabolism*; D000273:Adipose Tissue / Q000378:metabolism; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000276:immunology; D006801:Humans; D008969:Molecular Sequence Data; D009765:Obesity / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D019204:GTP-Binding Proteins