Distribution of the α-subunit of the Guanine Nucleotide-binding Protein G_i2 and its Comparison to Gα_o

Abstract

Site specific antisera against a synthetic peptide corresponding to the sequence 3–17 of Gαi2 have been raised and the specificity examined using purified homogeneous G_o, G_i2 and G_i containing a 41 kDa α-subunit. The distribution of Gα_i2 was investigated in plasma membranes from different tissues and cells and compared to the distribution of Gα_o and other pertussis toxin sensitive Gα. Considerable amounts of Gα_io were found in endocrine tissue especially in membranes from the adrenal and thyroid, in leucocytes and platelets where it constitutes the major, if not only, pertussis toxin-sensitive Gα, as well as in some cell lines (C6, NG 108–15, S49 cyc⁻); erythrocytes contained a 41 kDa Gα_i which was different from Gα_o. Gα_o was present abundantly in nervous tissue, adrenal medulla and cortex but also found in low amounts in other membranes except for lung, liver and blood cells. Subcellular fractionaltion of cardiac ventricular muscle demonstrated the presence of Gα_o and low amounts of Gα_i2 in sarcolemma, but only 41kDa Gα_i was present in sarcoplasmic reticulum. The importance of the distinct distribution in terms of signal transduction is discussed.