1. A new fluorescence assay for dipeptidylpeptidase IV using tripeptide L-prolyl-L-prolyl-L-alanine as substrate
K I Iijima, T Takei, M Hino, T Hayakawa J Biochem Biophys Methods. 1980 Aug;3(2):89-96. doi: 10.1016/0165-022x(80)90031-7.
We have developed a new fluorescence assay for dipeptidylpeptidase IV using a tripeptide, L-prolyl-L-prolyl-L-alanine, which might be one of the potential natural substrates. The principle of the assay is based on the measurement of fluorescent adduct between alanine liberated from the tripeptide by enzymatic hydrolysis and o-phthaldialdehyde in the presence of 2-mercaptoethanol in aqueous alkaline medium. This new assay is sensitive enough to measure the enzyme activity in as little as 0.01 microliter of human serum and in crevicular fluid obtained from human gingival sulcus. The Km value for the tripeptide was 1.7 x 10(-5) M which is less than one-tenth of that obtained with other chromogenic or fluorogenic substrates. The interference by serum was overcome by simply incorporating the same amount of serum in the standards.
3. Experimental charge density of L-alanyl-L-prolyl-L-alanine hydrate: classical multipole and invariom approach, analysis of intra- and intermolecular topological properties
Roman Kalinowski, Birger Dittrich, Christian B Hübschle, Carsten Paulmann, Peter Luger Acta Crystallogr B. 2007 Oct;63(Pt 5):753-67. doi: 10.1107/S0108768107030388. Epub 2007 Sep 14.
A high-resolution dataset of the tripeptide L-alanyl-L-prolyl-L-alanine hydrate was measured at 100 K using synchrotron radiation and CCD area detection. Electron densities were obtained from a full multipole refinement of the X-ray experimental data, from an invariom transfer and from a theoretical calculation. Topological and atomic properties were derived via an AIM analysis [Atoms in Molecules; see Bader (1990). Atoms in Molecules: A Quantum Theory, No. 22 in International Series of Monographs on Chemistry, 1st ed. Oxford: Clarendon Press] of these densities and compared with each other, as well as with results from the literature of other oligopeptides and amino acids. By application of the invariom formalism to a dataset of limited resolution, its performance was compared with a conventional spherical refinement, highlighting the possibility of aspherically modelling routine structure-determination experiments. The hydrogen-bonding scheme was subject to a detailed analysis according to the criteria of Koch & Popelier [(1995), J. Phys. Chem. 99, 9747-9754] as well as to the characterization of Espinosa et al. [(1998), Chem. Phys. Lett. 285, 170-173; (1999), Acta Cryst. B55, 563-572; (2002), J. Chem. Phys. 117, 5529-5542] using the results from the refined and invariom multipole densities as well as the spherical-density model, which are critically compared.