Factor V is a substrate for the transamidase factor XIIIa

Coagulation Factor V (Mr = 330,000), upon cleavage by thrombin, produces Factor Va, which is composed of two subunits with Mr values of 94,000 and 74,000, along with two activation fragments possessing no known function. Studies were undertaken to assess the ability of the transamidase Factor XIIIa to covalently incorporate the lysine analogs [3H]putrescine and dansylcadaverine into the thrombin-cleaved (activated) and unactivated forms of human and bovine Factor V. The incorporation of either probe into thrombin-activated Factor V proceeded at an initial rate approximately twice that for unactivated Factor V. The extent of the incorporation of [3H]putrescine or dansylcadaverine into activated or unactivated human Factor V was identical; 4 mol of either probe per mol of Factor V. In the case of bovine Factor V, however, while 4 mol of probe were bound per mol of the unactivated pro-cofactor, 5 mol of either lysine analog were covalently linked to 1 mol of thrombin-cleaved Factor V. Polyacrylamide gel fluorography, immunoaffinity chromatography, and immunoprecipitation identified the largest activation fragment of human Factor V (Mr = 150,000) and bovine Factor V (Mr = 120,000) to contain the sites of incorporation of the covalently bound probes. High molecular weight, apparently covalent polymers of Factor V were produced by the action of Factor XIIIa on activated and unactivated human or bovine Factor V. The absence of either probe in the reaction mixtures did not appear to allow an enhancement of protein polymerization.     

The molecular systematics of blowflies and screwworm flies (Diptera: Calliphoridae) using 28S rRNA, COX1 and EF-1α: insights into the evolution of dipteran parasitism

The Calliphoridae include some of the most economically significant myiasis-causing flies in the world - blowflies and screwworm flies - with many being notorious for their parasitism of livestock. However, despite more than 50 years of research, key taxonomic relationships within the family remain unresolved. This study utilizes nucleotide sequence data from the protein-coding genes COX1 (mitochondrial) and EF1α (nuclear), and the 28S rRNA (nuclear) gene, from 57 blowfly taxa to improve resolution of key evolutionary relationships within the family Calliphoridae. Bayesian phylogenetic inference was carried out for each single-gene data set, demonstrating significant topological difference between the three gene trees. Nevertheless, all gene trees supported a Calliphorinae-Luciliinae subfamily sister-lineage, with respect to Chrysomyinae. In addition, this study also elucidates the taxonomic and evolutionary status of several less well-studied groups, including the genus Bengalia (either within Calliphoridae or as a separate sister-family), genus Onesia (as a sister-genera to, or sub-genera within, Calliphora), genus Dyscritomyia and Lucilia bufonivora, a specialised parasite of frogs and toads. The occurrence of cross-species hybridisation within Calliphoridae is also further explored, focusing on the two economically significant species Lucilia cuprina and Lucilia sericata. In summary, this study represents the most comprehensive molecular phylogenetic analysis of family Calliphoridae undertaken to date.     

Grain legumes and green manures as pre-rice crops in Northeast Thailand

The loss of dry matter (ash corrected), nitrogen (N) and carbon (C) from residues of several tropical legume species was monitored using litter bags in the field over a three-month period in Northeast Thailand. This work was linked to an experiment in a farmers' field where the residual benefits of the same legume species grown before flooded rice were measured. Litter bags were incorporated in the flooded rice plots at the same time as residue incorporation in the field experiment. The species studied were Sesbania rostrata, Aeschynomene afraspera and a multi-purpose cowpea variety (Vigna unguiculata cv KVC-7). In the case of S. rostrata the breakdown of fresh and oven-dried residues and of residues buried at depths of 2–3 cm and 15 cm was also compared.Although the initial N and C concentrations were similar for all the residues they exhibited differing dry matter, N and C loss patterns. With Sesbania rostrata, 80% of the N was lost from the residues after 20 days, however, there was only a 40% decline in C and weight during the same period. The rate and amount of N loss from Aeschynomene afraspera residues was much less than with S. rostrata, declining by approximately 35% during the first 40 days. There were marked differences in rates of N loss from stem and leaves of A. afraspera indicating that monitoring the decomposition of stem and leaves combined can be misleading. In multi-purpose cowpea, loss patterns of dry matter, N and C were all similar and 50–65% was lost after 40 days burial. There was little difference between breakdown of fresh and oven-dried S. rostrata residues nor were there noticeable differences between residues incorporated superficially (2–3 cm) and buried at 15 cm. Although both %N and lignin:N ratios correlated well with weight and N loss from the residues, this was only the case when leaf and stem material were analyzed separately for A. afraspera.Despite the slower rate and smaller total amount of N released from the A. afraspera residues compared with the S. rostrata residues, a similar amount and proportion (around 20 kg N ha^-1 or 22–28%) of the N was recovered from both residues by a crop of rice planted at the time of residue incorporation. This suggests a considerably higher use efficiency by rice of the N released from the A. afraspera residues (approximately 40%) compared with that for S. rostrata (30%).     

Nitrogen fixation by groundnut and soyabean and residual nitrogen benefits to rice in farmers' fields in Northeast Thailand

Nitrogen fixation in groundnut and soyabean and the residual benefits of incoporated legume stover to subsequent rice crops were estimated in farmers' fields using¹⁵N-isotope methods. Three field experiments were conducted, two which examined N₂-fixation in groundnut by¹⁵N-isotope dilution using a non-nodulating groundnut as a reference crop and one in which N₂-fixation in two soyabean genotypes was compared using maize as the non-fixing reference crop. Groundnut fixed 72–77% of its N amounting to 150–200 kg N ha^-1 in 106–119 days and soyabean derived 66–68% of its N from N₂-fixation which amounted to 108–152 kg N ha^-1 under similar conditions. When legume stover was returned to the soil, there was a net contribution of N from N₂-fixing varieties of groundnut in all cases ranging from 13–100 kg N ha^-1, whilst due to the high % N harvest index in soyabean (87–88%) there was a net removal of N of 37–46 kg N ha^-1. In all cases if the legume stover was removed there was a net removal of N in the legume crop which ranged between 54 and 74 kg N ha^-1 in N₂-fixing varieties of groundnut and from 58 to 73 kg N ha^-1 in soyabean, whilst maize removed 66 kg N ha^-1 if its stover was returned and 101 kg N ha^-1 when the stover was removed. Growth of rice was improved in all cases where groundnut stover was returned resulting in increases in grain yield of 12–26% and increases in total dry matter production of 26–31%. Soyabean residues gave no increases in rice grain yield but increased total dry matter production by 12–20%. Rice accumulated more N in all cases where legume stover was returned to the soil, and N yields were larger in all cases after the N₂-fixing legumes than after the non-fixing reference crops. N difference estimates of the total residual N benefits from the N₂-fixing legumes ranged from 11–19 kg N ha^-1 after groundnut and 15–16 kg N ha^-1 after soyabean. The amounts of N estimated directly by application of¹⁵N-labelled stover amounted to 7.2–20.5 kg N ha^-1 with groundnut which represented recovery of 8–22% of the N added in the stover. In soyabean only 3.0–5.8 kg N ha^-1 was estimated to be recovered by¹⁵N-labelling which was 15–23% of the added N, whilst only 1.3 kg N ha^-1 (4% of the N added) was recovered by rice from the maize stover. An indirect¹⁵N-method based on addition of unlabelled stover to microplots where the soil had previously been labelled with¹⁵N gave extremely variable and often negative estimates of residual N benefits. Estimates of residual N from the added stover made by N difference calculations did not correspond with the estimates by direct¹⁵N-labelling in all cases and possible reasons for this are discussed.