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Rate zonal sedimentation gives information about the shape and size of proteins, and is useful for investigating protein-protein interactions. However, rate zonal sedimentation experiments typically last approximately 1 day. In contrast, this report describes a rate zonal sedimentation method requiring 1 h or less. This was accomplished by centrifuging small density gradients (200 microliters) prepared with sucrose or OptiPrep in a fixed-angle rotor at high relative centrifugal force. By using small gradient volumes, the sample dilution that occurs with larger gradients and with many chromatographic techniques was also avoided. For a variety of proteins, plots of S20,w versus distance sedimented during centrifugation in a TLA 120.2 rotor were linear. As a practical application, sedimentation of the heterotrimeric stimulatory G protein and its dissociated alpha-subunit were determined. The results were similar to those obtained with 17- to 22-h centrifugations in an SW 50.1 rotor and agreed with previously published values. Long periods of centrifugation might preclude the study of some unstable proteins or the investigation of protein-protein interactions whose affinities are to low to survive the lengthy centrifugations required to carry out traditional rate zonal sedimentation experiments. A rate zonal sedimentation technique that rivals many chromatographic methods in celerity will help to circumvent these problems.

Type IV adenylyl cyclase was synthesized in a cell-free coupled transcription and translation system. Radiolabeled type IV adenylyl cyclase was specifically immune precipitated with anti-ACIV antibodies. The molecular weight of in vitro translated type IV adenylyl cyclase was 110,000, similar to that for type IV adenylyl cyclase produced in the baculovirus system [B. Gao and A. G. Gilman, (1991) Proc. Natl. Acad. Sci. USA 88, 10178-10182]. Dimyristoyl phosphatidylcholine was required for efficient stimulation of activity by both forskolin and GS, with a maximum specific activity of 700 +/- 100 nmol cAMP.min-1.mg-1 attained with both effectors combined. Both bovine brain GS and in vitro translated GS alpha activated in vitro translated type IV adenylyl cyclase; however, G beta gamma only enhanced stimulation in the presence of in vitro translated GS alpha. Forskolin maximally activated at concentrations from 200 to 400 microM in the absence or presence of GS. The in vitro translated product was very stable as production of cAMP by forskolin/GS activated type IV adenylyl cyclase was linear for up to 90 min at 30 degrees C.