Ecosystem multifunctionality is more related to the indirect effects than to the direct effects of human management in China's drylands.

Drylands provide a wide range of important ecosystem functions but are sensitive to environmental changes, especially human management. Two major land use types of drylands are grasslands and croplands, which are influenced by intensive grazing activities and agricultural management, respectively. However, little is known about whether the ecosystem functioning of these two land use types is predominated affected by human management, or environmental factors (intrinsic environmental factors and factors modified by human management).

Soil Moisture and Soluble Salt Content Dominate Changes in Foliar δC and δN of Desert Communities in the Qaidam Basin, Qinghai-Tibetan Plateau.

Changing precipitation and temperature are principal drivers for nutrient cycling dynamics in drylands. Foliar isotopic carbon (C) and nitrogen (N) composition (δC and δN) are often used to describe the plant's water use efficiency and nitrogen use strategy in plant ecology research. However, the drivers and mechanisms under differential foliar δC and δN among plant species and communities are largely unknown for arid high-elevation regions.

Crystal structure of prothrombin reveals conformational flexibility and mechanism of activation.

The zymogen prothrombin is composed of fragment 1 containing a Gla domain and kringle-1, fragment 2 containing kringle-2, and a protease domain containing A and B chains. The prothrombinase complex assembled on the surface of platelets converts prothrombin to thrombin by cleaving at Arg-271 and Arg-320. The three-dimensional architecture of prothrombin and the molecular basis of its activation remain elusive.

Autoactivation of thrombin precursors.

Trypsin-like proteases are synthesized as inactive zymogens and convert to the mature form upon activation by specific enzymes, often assisted by cofactors. Central to this paradigm is that the zymogen does not convert spontaneously to the mature enzyme, which in turn does not feed back to activate its zymogen form. In the blood, the zymogens prothrombin and prethrombin-2 require the prothrombinase complex to be converted to the mature protease thrombin, which is unable to activate prothrombin or prethrombin-2.

Synthesis of α-Fe2O3 nanofibers for applications in removal and recovery of Cr(VI) from wastewater.

Purpose: Nanomaterials such as iron oxides and ferrites have been intensively investigated for water treatment and environmental remediation applications. The purpose of this work is to synthesize α-Fe(2)O(3) nanofibers for potential applications in removal and recovery of noxious Cr(VI) from wastewater.

Methods: α-Fe(2)O(3) nanofibers were synthesized via a simple hydrothermal route followed by calcination.

Crystallographic and kinetic evidence of allostery in a trypsin-like protease.

Protein allostery is based on the existence of multiple conformations in equilibrium linked to distinct functional properties. Although evidence of allosteric transitions is relatively easy to identify by functional studies, structural detection of a pre-existing equilibrium between alternative conformations remains challenging even for textbook examples of allosteric proteins. Kinetic studies show that the trypsin-like protease thrombin exists in equilibrium between two conformations where the active site is either collapsed (E*) or accessible to substrate (E).

The role of Zn2+ on the structure and stability of murine adenosine deaminase.

Adenosine deaminase (ADA) is a key enzyme in purine metabolism and crucial for normal immune competence. It is a 40 kDa monomeric TIM-barrel protein containing a tightly bound Zn(2+), which is required for activity. In this study, we have investigated the role of Zn(2+) with respect to ADA structure and stability.

Mutant N143P reveals how Na+ activates thrombin.

The molecular mechanism of thrombin activation by Na(+) remains elusive. Its kinetic formulation requires extension of the classical Botts-Morales theory for the action of a modifier on an enzyme to correctly account for the contribution of the E*, E, and E:Na(+) forms. The extended scheme establishes that analysis of k(cat) unequivocally identifies allosteric transduction of Na(+) binding into enhanced catalytic activity.

Structure and function of 2,3-dimethylmalate lyase, a PEP mutase/isocitrate lyase superfamily member.

The Aspergillus niger genome contains four genes that encode proteins exhibiting greater than 30% amino acid sequence identity to the confirmed oxaloacetate acetyl hydrolase (OAH), an enzyme that belongs to the phosphoenolpyruvate mutase/isocitrate lyase superfamily. Previous studies have shown that a mutant A. niger strain lacking the OAH gene does not produce oxalate.

Structure and function of PA4872 from Pseudomonas aeruginosa, a novel class of oxaloacetate decarboxylase from the PEP mutase/isocitrate lyase superfamily.

Pseudomonas aeruginosa PA4872 was identified by sequence analysis as a structurally and functionally novel member of the PEP mutase/isocitrate lyase superfamily and therefore targeted for investigation. Substrate screens ruled out overlap with known catalytic functions of superfamily members. The crystal structure of PA4872 in complex with oxalate (a stable analogue of the shared family alpha-oxyanion carboxylate intermediate/transition state) and Mg2+ was determined at 1.

Identification of fungal oxaloacetate hydrolyase within the isocitrate lyase/PEP mutase enzyme superfamily using a sequence marker-based method.

Aspergillus niger produces oxalic acid through the hydrolysis of oxaloacetate, catalyzed by the cytoplasmic enzyme oxaloacetate acetylhydrolase (OAH). The A. niger genome encodes four additional open reading frames with strong sequence similarity to OAH yet only the oahA gene encodes OAH activity.

Oxaloacetate hydrolase, the C-C bond lyase of oxalate secreting fungi.

Oxalate secretion by fungi is known to be associated with fungal pathogenesis. In addition, oxalate toxicity is a concern for the commercial application of fungi in the food and drug industries. Although oxalate is generated through several different biochemical pathways, oxaloacetate acetylhydrolase (OAH)-catalyzed hydrolytic cleavage of oxaloacetate appears to be an especially important route.

Structure and kinetics of phosphonopyruvate hydrolase from Variovorax sp. Pal2: new insight into the divergence of catalysis within the PEP mutase/isocitrate lyase superfamily.

Phosphonopyruvate (P-pyr) hydrolase (PPH), a member of the phosphoenolpyruvate (PEP) mutase/isocitrate lyase (PEPM/ICL) superfamily, hydrolyzes P-pyr and shares the highest sequence identity and functional similarity with PEPM. Recombinant PPH from Variovorax sp. Pal2 was expressed in Escherichia coli and purified to homogeneity.