The effect of sodium stearoyl lactylate on structural changes of wheat gluten in a model system fortified with inulin: Investigation with Fourier transform infrared spectroscopy

2019 ◽  
Vol 17 ◽  
pp. 100175 ◽  
Author(s):  
Amir Pourfarzad ◽  
Zahra Ahmadian ◽  
Mohammad Hossein Tavassoli-Kafrani
1998 ◽  
Vol 52 (2) ◽  
pp. 222-225
Author(s):  
Mamoru Hashimoto ◽  
Hiro-O Hamaguchi

The surface (about 130 molecular layers) of an oriented thin crystal of decanoic acid was subjected to sudden melting by a laser-induced temperature jump (T-jump), and the process of subsequent crystal re-growth was monitored by millisecond time-resolved multichannel Fourier transform infrared spectroscopy. The gauche–trans structural change of the alkane part of the molecule has been probed by the CH stretch bands in the 2800–3000 cm−1 region. The change in the molecular orientation has been detected by the OH stretch band around 3065 cm−1. The recovery curves for the CH2 antisymmetric stretch and the OH stretch bands are markedly different from each other in the first 200 ms, suggesting that the gauche–trans structural changes precedes the crystal re-growth. After 500 ms, the recovery curves become identical. This result means that the rate of the gauche to the trans structural change is equal to the rate of the recovery of the molecular orientation. It is highly likely that a fast equilibrium is attained between the gauche and the trans conformations in the liquid phase after 500 ms from the sudden melting and that the crystal re-growth takes place solely via the all-trans structure in the liquid phase.


2004 ◽  
Vol 279 (44) ◽  
pp. 46226-46233 ◽  
Author(s):  
Partha P. Chakrabarti ◽  
Yan Suveyzdis ◽  
Alfred Wittinghofer ◽  
Klaus Gerwert

GTPaseactivatingproteins (GAPs) down-regulate Ras-like proteins by stimulating their GTP hydrolysis, and a malfunction of this reaction leads to disease formation. In most cases, the molecular mechanism of activation involves stabilization of a catalytic Gln and insertion of a catalytic Arg into the active site by GAP. Rap1 neither possesses a Gln nor does its cognate Rap-GAP employ an Arg. Recently it was proposed that RapGAP provides a catalytic Asn, which substitutes for the Gln found in all other Ras-like proteins (Daumke, O., Weyand, M., Chakrabarti, P. P., Vetter, I. R., and Wittinghofer, A. (2004)Nature429, 197–201). Here, RapGAP-mediated activation has been investigated by time-resolved Fourier transform infrared spectroscopy. Although the intrinsic hydrolysis reactions of Rap and Ras are very similar, the GAP-catalyzed reaction shows unique features. RapGAP binding induces a GTP*conformation in which the three phosphate groups are oriented such that they are vibrationally coupled to each other, in contrast to what was seen in the intrinsic and the Ras·RasGAP reactions. However, the charge shift toward β-phosphate observed with RasGAP was also observed for RapGAP. A GDP·Piintermediate accumulates in the GAP-catalyzed reaction, because the release of Piis eight times slower than the cleavage reaction, and significant GTP synthesis from GDP·Piwas observed. Partial steps of the cleavage reaction are correlated with structural changes of protein side groups and backbone. Thus, the Rap·RapGAP catalytic machinery compensates for the absence of acis-Gln by atrans-Asn and for the catalytic Arg by inducing a different GTP conformation that is more prone to be attacked by a water molecule.


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