Release of guanosine triphosphate binding protein α subunits from mouse myocardial membranes: Basic properties and their alterations in acute murine chagas disease

Objective: The aim was to investigate the arrangement of heterotrimeric αβγ G proteins in myocardial membranes using GTPγS dependent release characteristics of their α subunits in acute murine Chagas disease. Methods: The properties of GTPγS dependent α subunit release were monitored immunochemically as well as by cholera toxin and pertussis toxin catalysed [³²P]ADP ribosylation. Results: GTPγS, as opposed to other nucleotides, caused optimal and virtually instantaneous release of soluble 40 kDa [³²P]ADP ribosylated protein in pertussis toxin treated membranes. When determined immunochemically, infection decreased both the sensitivity to GTPγS dependent release of αi subunits and appeared to facilitate the appearance of GTPγS dependent release of αi₃. GTPγS also caused the release of soluble 45 and 40 kDa proteins as detected by cholera toxin-[³²P]ADP ribosylated membranes and immunochemical analysis. With regard to cholera toxin-[³²P]ADP ribosylated Gs substrates sensitive to GTPγS dependent release, infection (1) decreased the amount of 45 kDa as protein, (2) increased the amount of 40 kDa protein, and (3) enhanced sensitivity to GTPγS. In contrast, there was no effect of infection on the magnitude or sensitivity to GTPγS dependent release of immunochemical αS. Conclusions: The diverse characteristics of GTPγS dependent release of the very similar α subunits from myocardial membranes and their unique sensitivity to infection with T cruzi. suggest that these very similar proteins are arranged within the plasma membrane in such a manner as to modify their biochemical behaviour.