Preparation and characterization of a pH-responsive nanogel based on a photo-cross-linked micelle formed from block copolymers with controlled structure.

Poly(ethylene glycol)-b-poly(2-(diethylamino)ethyl methacrylate-co-2-cinnamoyloxyethyl acrylate) (PEG-b-P(DEAEMA/CEA)) was prepared by reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. As solution pH is increased from an acidic pH, the hydrodynamic radius (R(h)) increases abruptly near pH 7, indicative of the micelle formation at pH > 7. The micelle formation at pH > 7 was supported by (1)H NMR and light scattering data. Upon irradiation of light, polymer chains in the core of the polymer micelle are cross-linked as a result of the photodimerization of the cinnamoyl groups, yielding a nanogel. The nanogel was characterized by gel-permeation chromatography (GPC), light scattering, small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and fluorescence techniques. The nanogel displayed an ability to solubilize N-phenyl-1-naphthylamine (PNA) and 1-pyrenemethanol (hydrophobic guest molecules) into the hydrophobic core at pH > 7. It was confirmed with PNA that the solubilization of a guest molecule occurred at polymer concentrations (C(p)) lower than the critical micelle concentration (cmc) for PEG-b-P(DEAEMA/CEA) because the nanogel retains its micellar structure at C(p) < cmc. 1-Pyrenemethanol is strongly captured by the nanogel at pH 10, whereas it is easily released from the nanogel when pH is reduced to 3. This indicates that the hydrophobicity of the core of the nanogel can be modulated by a change in the degree of protonation of the DEAEMA units in the core, and thus the capture of a guest molecule and its release can be controlled by a change in solution pH.

The metal-binding motif of dipeptidyl peptidase III directly influences the enzyme activity in the copper derivative of dipeptidyl peptidase III.

The zinc-binding motif (HELLGH) of dipeptidyl peptidase III (DPP III) is different from the common zinc-binding motif (HExxH) of metallopeptidases. To clarify the importance of the zinc-binding motif part of DPP III for enzymatic activity, we measured the recovery of the enzyme activity of apo-Leu(453)-deleted dipeptidyl peptidase III (apo-Leu(453)-del-DPP III), which has a motif (HELGH) like that of the common peptidase (HExxH), in the presence of various metal ions. The enzyme activity of apo-Leu(453)-deleted DPP III could not be recovered by the addition of cupric ions, while apo-DPP III could be easily reactivated by the addition of cupric ions. The visible and electron paramagnetic resonance spectra of the isolated Cu(II)-Leu(453)-del DPP III clearly show that the cupric ions of Cu(II)-Leu(453)-del-DPP III bound to the motif part (HELGH) but did not exhibit any enzyme activity. The motif part of DPP III directly influences the expression of the enzyme activity in the copper derivative of DPP III. The competitive inhibitor that is not at all digested by DPP III, Hisprophen (His-Pro-Phe-His-Leu-d-Leu-Val-Tyr), has been determined. The inhibition constant (K(i)) of Hisprophen for DPP III or Cu(II)-DPP III was 4.1x10(-5) or 3.8x10(-5)M, respectively. In the presence of the competitive peptide inhibitor, Hisprophen, the EPR spectra of Cu(II)-DPP III were completely different from that of Cu(II)-DPP III itself. This result clearly indicates that the metal ions of DPP III are located in the active site and directly interact with the substrate.