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The radius of gyration Rg, the hydrodynamic radius Rh, and the intrinsic viscosity [η] have been measured for polystyrene in cyclohexane (at the θ temperature and 44.5°C), 2‐butanone (at 30°C), and toluene (at 30°C) in the molecular weight range 2.38 × 105 ≤ Mw ≤ 5.47 × 106 to elucidate the excluded‐volume effects on dynamical behavior in dilute polymer solutions in the crossover region from θ to good‐solvent conditions. The results are compared with theoretical predictions of current thermal blob theories and the Pade approximant theory of Tanaka. It is found that the ratio of Rh/Rg decreases with an increase in the excluded‐volume effect, following the prediction of the simple blob theory, but that its magnitude is about 15% higher than the theoretical value. Experimental variation of [η] with Rh and/or Rg lies in between predictions of the scaling law and the Pade approximant. The concentration dependence of the diffusion coefficient is also compared with predictions of current theories.

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The type I diacylglycerol kinase (DGK) isozymes (α, β and γ) contain a shared recoverin homology (RVH) domain, a tandem repeat of Ca2+-binding EF-hand motifs, two cysteine-rich C1 domains, and the catalytic domain. We previously reported that a DGKα mutant lacking the RVH domain and EF-hands was constitutively active, implying that the N-terminal region (NTR) of DGKα, consisting of the RVH domain and EF-hand motifs, intramolecularly interacts with and masks the activity of the C-terminal region (CTR), containing the C1 and catalytic domains. In this study, we demonstrate that a glutathione S-transferase (GST)-fused DGKα-NTR construct physically binds to a green fluorescent protein (GFP)-fused DGKα-CTR construct. Moreover, co-precipitation of GFP-DGKα-CTR with GST-DGKα-NTR was clearly attenuated by the addition of 1 μM Ca2+. This result indicates that Ca2+ induces dissociation of the physical interaction between DGKα-NTR and DGKα-CTR. In addition to previously reported calcium-dependent changes in the hydrophobicity and net surface charge, Ca2+ also appeared to induce a decrease in the α-helical content of DGKα-NTR. These results suggest that Ca2+-induced conformational changes in the NTR release the intramolecular association between the NTR and the CTR of DGKα.

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