Structure and thermal history dependant phase behavior of hydrated synthetic sphingomyelin analogue: 1,2-dimyristamido-1,2-deoxyphosphatidylcholine

The physical properties of hydrated multilamellar sample of 1,2-dimyristamido-1,2-deoxyphosphatidylcholine (DDPC) were investigated by means of differential scanning calorimetry (DSC), static X-ray diffraction, and simultaneous DSC and X-ray diffraction. The DDPC is a synthetic sphingomyelin analogue and has two amide bonds in its hydrophobic parts. This paper reports on metastable phase behavior of the hydrated DDPC sample. By cooling from a chain-melted state at the rates of greater than 4 oC min-1, hydrated DDPC bilayers form a metastable gel phase. In the gel phase, the hydrophobic chains are tilted with respect to the bilayer normal, as like the gel phase of glycero-phosphatidylcholines. By heating, the metastable gel phase is transformed in to a stable phase associated with an exothermic heat event at 18.3 oC (DH = 14.6 kJ mol-1) and then the stable phase is transformed into a liquid-crystalline phase at 25.6 oC (DH = 42 kJ mol-1). The incubation at 17 oC for more than 1 hour also induces the formation of the stable phase. In the stable phase, the hydrophobic chains are packed into highly ordered crystal-like structure. However, the X-ray diffraction pattern of the stable phase suggested that the entire DDPC molecules do not form a two-dimensional molecular ordered lattice, differing from normal subgel phase of glycero-phosphatidylcholines. The structure and phase behavior of DDPC revealed by the present study are discussed from the viewpoint of hydrogen bonds

Configuration of the active Mg-ATP complex in protein kinase C reaction

AbstractTo probe the active site structure of protein kinase C stereochemical studies were carried out by using ATPβs. The enzyme utilizes either one of the diastereomers (Sp and Rp) of ATPβs almost equally well as a substrate. This result contrasts with that for cyclic AMP-dependent protein kinase, suggesting that the topography of the nucleotide-binding site is significantly different between the two kinases

Catalytic Efficiency of [20]Paracyclophane Oxime and Cycloheptaamylose in the Decomposition of Carboxylate and Carbonate Esters

The hydrolytic decomposition of dodecyl ρ-nitrophenyl carbonate (LPNC) and ρ-nitrophenyl dodecanoate (PNPL) as mediated by 10-hydroxy-ll-hydroxyimino[20]-paracyclophane (Oxime-I) and cycloheptaamylose (β-CD) has been investigated in aqueous media containing 9.9% (v/v) ethanol and 1.0% (v/v) acetonitrile to gain an insight into the reaction and/or substrate specificity. Both LPNC and PNPL were decomposed effectively by an equimolar amount of Oxime-I. It turned out from the analysis of kinetic data that the binding of LPNC to Oxime-I is 2.5 times tighter than that of PNPL, but the subsequent catalysis is 3.3 times more favorable for PNPL than for LPNC. Hence, the overall efficiency of Oxime-I is 1.3 times greater for PNPL, as changed from a 13-fold difference between both substrates in the simple alkaline hydrolysis. β-CD was found to be effective also in the decomposition of LPNC when added in large excess over substrate. Comparison of kinetic parameters between the two systems, Oxime-I and β-CD, indicated that the former is better in both binding and catalytic effects toward the extremely hydrophobic substrates