Characterization of the tryptophan environments of interleukins 1 alpha and 1 beta by fluorescence quenching and lifetime measurements

The tryptophan environments of interleukins 1 alpha and 1 beta, immunomodulatory proteins with similar biological activities but only 25% sequence homology, were characterized by steady-state and dynamic fluorescence measurements. Both proteins exhibited similar emission maxima, but the emission intensity of IL-1 beta was greatly enhanced by increasing the ionic strength of the medium, whereas that of IL-1 alpha was unaffected. The two cytokines were also similarly quenched by the polar quencher acrylamide, but differences were observed for the ionic quenchers iodide and cesium. The fluorescence intensity decays of both cytokines were characterized by two (long and short) component lifetimes. However, the average lifetime of IL-1 beta (4.4 ns) was much longer than that of IL-1 alpha (1.93 ns). Taken together with the results of steady-state measurements, we suggest that the single tryptophan of IL-1 beta is statically quenched by neighboring charged residues, whereas the tryptophan fluorescence of IL-1 alpha is unaffected by ionic strength, and that the tryptophans of the two proteins have different accessibilities to ionic quenchers. The results are discussed in terms of similarities and differences in the tryptophan environments of the two proteins.     

Daily changes in the sensitivity of wax-moth larvae, Galleria mellonella, to cooling stress

ABSTRACT. Sensitivity to cooling stress in the last instar larvae of Galleria mellonella was measured as (a) the number of extra larval moults, (b) the number of larvae retaining the ability to secrete silk, and (c) the number showing arrested development. With respect to (a) and (b) there were considerable differences in sensitivity across the day. A relationship was observed between the number of additional larval moults induced by chilling and the ability of prepupal larvae to spin silk: the periods during the 24 h when the most larvae passed through additional larval moults were periods characterized by the smallest number of larvae capable of spinning, and vice versa. These daily changes were apparently partly independent of developmental age. Daily variations in sensitivity also occurred when larvae of the same age were cooled at different times of day. It is suggested that these rhythms in cold-sensitivity are related to a cold-sensitive rhythm in juvenile hormone secretion, or hormone sensitivity in the tissues.     

How sympatric is speciation in the Howea palms of Lord Howe Island?

The two species of the palm genus Howea (Arecaceae) from Lord Howe Island, a minute volcanic island in the Tasman Sea, are now regarded as one of the most compelling examples of sympatric speciation, although this view is still disputed by some authors. Population genetic and ecological data are necessary to provide a more coherent and comprehensive understanding of this emerging model system. Here, we analyse data on abundance, juvenile recruitment, pollination mode and genetic variation and structure in both species. We find that Howea forsteriana is less abundant than Howea belmoreana . The genetic data based on amplified fragment length polymorphisms markers indicate similar levels of variation in the two species, despite the estimated census population size of H. belmoreana being three times larger than that of H. forsteriana . Genetic structure within species is low although some weak isolation by distance is detectable. Gene flow between species appears to be extremely limited and restricted to early-generation hybrids – only three admixed individuals, classified as F2s or first generation backcrosses to a parental species, were found among sampled palms. We conclude that speciation in Howea was indeed sympatric, although under certain strict definitions it may be called parapatric.