The three-dimensional structures of mouse epidermal growth factor (53 residues) in pH 2.1 and pH 6.8 solutions were determined by two-dimensional NMR and distance geometry calculation. Ten structures that satisfied the NMR-derived distance constraints were obtained for each pHs using XPLOR program. The topology of the main chain was identical at both pHs, but the global shape at pH 6.8 was found to be more compact than that at pH 2.1.
The motion of catalytic residues and water molecules in the active site of acyl-chymotrypsin was studied with stochastic boundary molecular dynamics. A water molecule expected to provide the nucleophilic OH- for the deacylation reaction was found trapped between His57 and the ester linkage of the acyl group. The trapped water oxygen and hydrogen occasionally approach the carbonyl carbon and the ester oxygen, respectively, while keeping the hydrogen bond to His57 Nε2. Such configurations lead us a stepwise mechanism with very small imidazole movement or one step mechanism in which the tetrahedral intermediate is at the saddle point of the reaction.
Enkephalin is a morphine-like pentapeptide: Tyr-Gly-Gly-Phe-Xxx, Xxx=Met or Leu. To consider the relationship between the enkephalin conformation and the opioid receptor, the crystal structures of enkephalin analogues were analyzed by the X-ray diffraction method, and two characteristic forms were observed as the fundamental conformation of enkephalin, One is the β-turn structllre and the other the antiparallelly extended dimer (ED) structure. From the NMR and CD spectral studies, it was suggested that the β-turn and ED structures of enkephalin are the most probable conformations for the binding to μ-and δ-receptors, respectively. Further, the molecular-dynamics simulations indicated that these conformation are both advantageous in energetical term. Based on the insight of the enkephalin conformation, it was attempted to convert the μ-selective morphine toward δ-affinitive ligand by the dimerization.
Adherens junctions offer an advantageous model for analyzing the molecular basis of actinmembrane interaction. We have succeeded in isolating the cell-to-cell adherens junctions from rat liver. This article reviews our recent studies on the molecular organization of the undercoat of the isolated adherens junctions.
Intracellular lipid traffic was studied using fluorescent lipid analogs. 1) Fluorescent ceramide analog was metabolized in the Golgi apparatus and transported to the plasma membrane most likely via vesicular traffic. 2) Phosphatidylcholine liposomes were shown to fuse with the Golgi apparatus in an ATP-dependent manner. 3) Exogenous fluorescent phosphatidylserine analog was transported to mitochondria through the Golgi apparatus. Involvement of plasma membrane "flippase" in the uptake of exogenous phosphatidylserine was suggested.
This article briefly reviews the mechanism of ATP synthesis by mitochondria. The interaction of dicyclohexylcarbodiimide of oligomycin at the membrane sector (F0) of the ATP synthase complex alters the mode of ATP binding at the catalytic sites of F1. The rate of energy production by the respiratory chain modulates the kinetics of ATP synthesis between a low Km-low Vmax mode and a high Km-high Vmax mode. The turnover number of the ATP synthase in the direction of ATP synthesis was determined to be 440s-1. Finally, kinetic and equilibrium binding studies have shown that three molecules of ADP bind to the ATP synthase in a sequential manner before rapid ATP synthesis ensues.
Gymnemic acids, a mixture of triterpene glucuronides extracted from the Indian plant Gymnema sylvestre, have been known to suppress the sweet taste sensation in man. Recent studies have revealed that gymnemic acids showed inhibitory effects not only on glucose absorption in the rat small intestine, but also on glucan synthesis by glucosyltransferase from Streptococcus mutans. These findings suggest that gymnemic acids interact with various proteins which take part in sugar discriminations.
CaMV genome is a circular and double stranded DNA. But it uses RNA (35S RNA) as a replicative intermediate and employs reverse transcriptase for genome replication. During the replication process via reverse transcription, there are some possibilities to rearrange the genome construction. Such possibilities are usually suppressed but seem to be advantageous to the evolution.
Retinoid compound was involed in the photoperiodic photoreception in the induction of egg-diapause of the silkworm and, retinal and 3-OH-retinal were found in the brain of a possible photoreceptor. GABAergic neurones regulated the secretion of diapause hormone from the suboeso-phageal ganglion.