Cation Modulation of Hemoglobin Interaction with Sodium n-Dodecyl Sulfate (SDS). I: Calcium Modulation at pH 7.20

Application of merged spectroscopic data combined with chemometric analysis for resolution of hemoglobin intermediates during chemical unfolding

Using tetradecyltrimethylammonium bromide (TTAB) as a surfactant denaturant, and augmentation of different spectroscopic data, helped to detect the intermediates of hemoglobin (Hb) during unfolding process. UV-vis, fluorescence, and circular dichroism spectroscopy were used simultaneously to monitor different aspects of hemoglobin species from the tertiary or secondary structure points of view. Application of the multivariate curve resolution-alternating least square (MCR-ALS), using the initial estimates of spectral profiles and appropriate constraints on different parts of augmented spectroscopic data, showed good efficiency for characterization of intermediates during Hb unfolding. These results indicated the existence of five protein species, including three intermediate-like compounds in this process. The unfolding pathway in the presence of TTAB included conversion of oxyhemoglobin into deoxyhemoglobin, and then ferrylhemoglobin, ferrihemoglobin or aquamethemoglobin, which finally transformed into hemichrome. This is the first application of chemometric analysis on the merged spectroscopic data related to chemical denaturation of a protein. These types of analysis in multisubunit proteins not only increase the domain of information, but also can reduce the ambiguities of the obtained results.

Hydrogen peroxide sensitive hemoglobin-capped gold nanoclusters as a fluorescence enhancing sensor for the label-free detection of glucose

A novel label-free fluorescent probe based on blue-emitting gold nanoclusters capped by hemoglobin for the direct detection of glucose is presented.

A novel electrochemical hydrogen peroxide biosensor based on hemoglobin capped gold nanoclusters–chitosan composite

In this work, the first direct electrochemistry of Hb-AuNCs and its electrocatalysis towards H₂O₂ in a biosensing system has been reported.

Heme degradation upon production of endogenous hydrogen peroxide via interaction of hemoglobin with sodium dodecyl sulfate

In this study the hemoglobin heme degradation upon interaction with sodium dodecyl sulfate (SDS) was investigated using UV-vis and fluorescence spectroscopy, multivariate curve resolution analysis, and chemiluminescence method. Our results showed that heme degradation occurred during interaction of hemoglobin with SDS producing three fluorescent components. We showed that the hydrogen peroxide, produced during this interaction, caused heme degradation. In addition, the endogenous hydrogen peroxide was more effective in hemoglobin heme degradation compared to exogenously added hydrogen peroxide. The endogenous form of hydrogen peroxide altered oxyHb to aquamethemoglobin and hemichrome at low concentration. In contrast, the exogenous hydrogen peroxide lacked this ability under same conditions.

Cation modulation of hemoglobin interaction with sodium n-dodecyl sulfate (SDS). III: Calcium interaction with R- and mixed spin states of hemoglobin S at pH 5.0: the musical chair paradox

We investigate the interaction of Ca(2+) (0-500 µM) and a membrane mimic (0.60 mM SDS) with both the R- and mixed spin states hemoglobin S (HbS) as a function of time. These interactions were carried out at pH 5.0. We aim at ascertaining if there is or are differences in the UV-Visible spectra of such interactions to account for the dynamics of calcium ion concentrations [Ca(2+)] in initiating structures which may ultimately suggest HbS polymerization and or resistance to Plasmodium attack. From our results, we conclude that (a) simultaneous interaction of 40 µM Ca(2+) and 0.60 mM SDS with the R state protein would promote structural formations that can "lock up" the protein for nucleation on the membranes and or become cytotoxic to the parasite; (b) simultaneous R state HbS-SDS or R state HbS-Ca(2+) would lead to enhanced hemin formation and less deoxyHb species. This condition is unlikely to precipitate polymerization in the HbS but the resulting hemin would poison the parasite; (c) the mixed spin state HbS-SDS and 40 µM Ca(2+) interaction yields more toxic products to that of the interaction of the mixed spin HbS-SDS with 500 µM Ca(2+) thus suggesting why the 40 µM Ca(2+) is important in parasite Hb proteolysis; and (d) pronounced structural changes on interaction with SDS and Ca(2+) are more in the R state to the mixed spin state.

Kinetic Analysis of Guanidine Hydrochloride Inactivation of β-Galactosidase in the Presence of Galactose

Inactivation of purified β-Galactosidase was done with GdnHCl in the absence and presence of varying [galactose] at 50°C and at pH 4.5. Lineweaver-Burk plots of initial velocity data, in the presence and absence of guanidine hydrochloride (GdnHCl) and galactose, were used to determine the relevant K_m and V_max values, with p-nitrophenyl β-D-galactopyranoside (pNPG) as substrate, S. Plots of ln([P]_∞ − [P]_t) against time in the presence of GdnHCl yielded the inactivation rate constant, A. Plots of A versus [S] at different galactose concentrations were straight lines that became increasingly less steep as the [galactose] increased, showing that A was dependent on [S]. Slopes and intercepts of the 1/[P]_∞ versus 1/[S] yielded k₊₀ and k'₊₀, the microscopic rate constants for the free enzyme and the enzyme-substrate complex, respectively. Plots of k₊₀ and k'₊₀ versus [galactose] showed that galactose protected the free enzyme as well as the enzyme-substrate complex (only at the lowest and highest [galactose]) against GdnHCl inactivation. In the absence of galactose, GdnHCl exhibited some degree of non-competitive inhibition. In the presence of GdnHCl, galactose exhibited competitive inhibition at the lower [galactose] of 5 mM which changed to non-competitive as the [galactose] increased. The implications of our findings are further discussed.