‘Swell Dialysis’ Demonstrates that Adenylate Cyclase in Trypanosoma brucei is Regulated by Calcium Ions

Abstract

A new technique, ‘swell dialysis’, is described that allows the study of cellular enzymes in situ if they are located in the cytoplasm or on the cytoplasmic face of any membrane. The technique is potentially applicable to any population of individual eukaryotic cells that lack a cell wall. In this study swell dialysis has been applied to an examination of the regulation of adenylate cyclase in bloodstream forms of Trypanosoma brucei (427-12/ICI-060). Adenylate cyclase in this protozoon is shown to be controlled by Ca²⁺. There is a 16-fold stimulation of the cyclase at 100 μM Ca²⁺ over basal activity without added Ca²⁺. The ability of Ca²⁺ to stimulate adenylate cyclase is lost upon rupture of the cell, which is reminiscent of the loss of control of the adenylate cyclase in Escherichia coli by sugars of the phosphotransferase system when cell breakage occurs. The physiological function of the Ca²⁺ activation of adenylate cyclase in T. brucei has not been established but a possible role in the change of surface coat in bloodstream forms should be considered.