Kinetic studies on coenzyme binding and coenzyme dissociation in tryptophanase immobilized on sepharose

Quantitative Galactose Colorimetric Competitive Assay Based on Galactose Dehydrogenase and Plasmonic Gold Nanostars

We describe a competitive colorimetric assay that enables rapid and sensitive detection of galactose and reduced nicotinamide adenine dinucleotide (NADH) via colorimetric readouts and demonstrate its usefulness for monitoring NAD+-driven enzymatic reactions. We present a sensitive plasmonic sensing approach for assessing galactose concentration and the presence of NADH using galactose dehydrogenase-immobilized gold nanostars (AuNS-PVP-GalDH). The AuNS-PVP-GalDH assay remains turquoise blue in the absence of galactose and NADH; however, as galactose and NADH concentrations grow, the reaction well color changes to a characteristic red color in the presence of an alkaline environment and a metal ion catalyst (detection solution). As a result, when galactose is sensed in the presence of H2O2, the colored response of the AuNS-PVP-GalDH assay transforms from turquoise blue to light pink, and then to wine red in a concentration-dependent manner discernible to the human eye. This competitive AuNS-PVP-GalDH assay could be a viable analytical tool for rapid and convenient galactose quantification in resource-limited areas.

Feasibility of NAD(P)/NAD(P)H as redox agents in enzymatic plasmonic gold nanostar assays for galactose quantification

Plasmonic colorimetric sensors have emerged as powerful analytical tools in biochemistry due to their localized surface plasmon resonance extinction in the visible range. Here, we describe the feasibility of NAD(P)/NAD(P)H as redox agents in enzymatic plasmonic gold nanostar (AuNS) assays for galactose quantification using three model enzymes, GalDH, AR and GalOx, immobilized separately on polyvinylpyrrolidone-capped AuNS scaffolds. These highly specific, sensitive and selective bioassays induce the transformation of AuNS into quasi-spherical nanoparticles during the biorecognition of galactose in water and synthetic blood matrices. As a result, using our inexpensive and simple AuNS plasmon bioassays, the presence of galactose may be detected spectrophotometrically and by the naked eye.

Hydrolysis of fibrinogen and plasminogen by immobilized earthworm fibrinolytic enzyme II from Eisenia fetida

Earthworm fibrinolytic enzyme II (EFE-II) from Eisenia fetida has a broad hydrolytic specificity for peptide bonds. Our experiments show that EFE-II can hydrolyze the specific chromogenic substrates of thrombin (Chromozym TH), trypsin (Chromozym TRY) and elastase (Chromozym ELA). The Michaelis-Menten constant (K(m)) for Chromozym ELA (approximately 245 microM) is much higher than those for the thrombin (approximately 90 microM) and trypsin (approximately 60 microM) substrates. On the other hand, EFE-II is inhibited most strongly by soybean trypsin inhibitor (SBTI), and weakly inhibited by elastinal, suggesting that EFE-II has a trypsin-like activity. Degradation of plasminogen (PLg) and fibrinogen by EFE-II was investigated after EFE-II had been immobilized onto 1,1'-carboryl-diimidazole (CDI)-activated Sepharose CL-6B. The immobilized EFE-II has 55-60% activity of the native enzyme with a higher thermal and pH resistance. EFE-II cleaves PLg at four hydrolytic sites: Lys(77)-Arg(78), Arg(342)-Met(343), Ala(444)-Ala(445) and Arg(557)-Ile(558). The site Arg(557)-Ile(558) is also recognized and cleaved by tissue plasminogen activator (t-PA) and urokinase (UK), producing active plasmin. Cleaving Ala(444)-Ala(445) released mini-plasmin with secondary activity to hydrolyze fibrin. Immobilized EFE-II degrades not only the Aalpha chain of fibrinogen in the C-terminal region (like human neutrophil elastase, HNE), but also in the N-terminal region at the Val(21)-Glu(22) site.