Observation of the developing optical continuum along a nonlinear waveguide.

We describe what is to our knowledge the first nondestructive measurement of the evolution of an optical continuum as a function of distance along a nonlinear waveguide. Spectral mapping is achieved on a subwavelength scale by utilizing near-field microscopy to probe the waveguide's evanescent field. The measured continuum broadening along the waveguide agrees in general form with predictions of broadening from theoretical calculations, but differs in some important details. Subwavelength resolution measurements are made both along and across the waveguide to reveal spectral variations not seen before by other techniques.

Complete cDNA sequence of SAP-like pentraxin from Limulus polyphemus: implications for pentraxin evolution.

The serum amyloid P component (SAP)-like pentraxin Limulus polyphemus SAP is a recently discovered, distinct pentraxin species, of known structure, which does not bind phosphocholine and whose N-terminal sequence has been shown to differ markedly from the highly conserved N terminus of all other known horseshoe crab pentraxins. The complete cDNA sequence of Limulus SAP, and the derived amino acid sequence, the first invertebrate SAP-like pentraxin sequence, have been determined. Two sequences were identified that differed only in the length of the 3' untranslated region. Limulus SAP is synthesised as a precursor protein of 234 amino acid residues, the first 17 residues encoding a signal peptide that is absent from the mature protein. Phylogenetic analysis clusters Limulus SAP pentraxin with the horseshoe crab C-reactive proteins (CRPs) rather than the mammalian SAPs, which are clustered with mammalian CRPs. The deduced amino acid sequence shares 22% identity with both human SAP and CRP, which are 51% identical, and 31-35% with horseshoe crab CRPs. These analyses indicate that gene duplication of CRP (or SAP), followed by sequence divergence and the evolution of CRP and/or SAP function, occurred independently along the chordate and arthropod evolutionary lines rather than in a common ancestor. They further indicate that the CRP/SAP gene duplication event in Limulus occurred before both the emergence of the Limulus CRP variants and the mammalian CRP/SAP gene duplication. Limulus SAP, which does not exhibit the CRP characteristic of calcium-dependent binding to phosphocholine, is established as a pentraxin species distinct from all other known horseshoe crab pentraxins that exist in many variant forms sharing a high level of sequence homology.

Birefringent Fresnel zone plates in silica fabricated by femtosecond laser machining.

We demonstrate maskless, single-step fabrication of strongly birefringent Fresnel zone plates by focusing of femtosecond laser pulses deep within silica substrates. The process allows us to produce alternate zone rings directly by inducing a local refractive-index modification of the order of n~10(-2) . The embedded zone plates shown in this Letter exhibit efficiencies that vary by as much as a factor of ~6 for orthogonal polarizations. Focal lengths of primary and secondary foci are shown to compare well with theory.

Regulation of pigment content and enzyme activity in the cyanobacterium Nostoc sp. Mac grown in continuous light, a light-dark photoperiod, or darkness.

Both short-term and long-term adaptations of cyanobacterial metabolism to light and dark were studied in Nostoc sp. Mac. Long-term adaptations were induced by growing cells in the presence of glucose under (a) 30 µE m-2 s-1 continuous white light, (b) under a 14/10 h light/dark cycle, or (c) complete darkness. Short-term regulation of enzyme activities by light was then studied in cells rendered osmotically fragile with lysozyme. Cells were briefly illuminated then enzyme activities were measured following rapid lysis in a hypotonic assay medium. The following results were obtained. (1) Relative to fresh weight, dark-grown cells contained less chlorophyll, much less phycoerythrin, but similar amounts of phycocyanin compared to cells grown under either light regime. Relative to chlorophyll, the higher phycocyanin and much lower phycoerythrin in the dark-grown vs light-grown cells resembles long term changes in pigment content that occur during complementary chromatic adaptation to red vs orange light. (2) Both dark and light/dark grown cells displayed generally lowered photosynthetic activities compared to light-grown cells. The exception to this was the activity of fructose 1,6-bisphosphatase, which was higher in dark-grown cells. However, the photosynthetic induction period was markedly shorter in the light/dark-grown cells indicating an adaptation to changing illumination during growth. (3) Inhibitor studies using methyl viologen show that the fructose 1,6-bisphosphatase is reversibly light-activated in vivo by the cyanobacterial thioredoxin system under all growth conditions. Glucose-6-phosphate dehydrogenase activity was detected in cells grown in all conditions and this activity was reversibly deactivated by light or by dithiothreitol. In contrast, the protonmotive ATPase F0F1-type ATPase was fully active in both light and dark-adapted cells regardless of the light regime used for growth. (4) It is concluded that the Calvin cycle enzymes, their short-term regulatory system, including thioredoxin, glucose-6-phosphate dehydrogenase and an F0F1 ATPase not under thioredoxin control, are expressed in cells grown in complete darkness. Adaptation to heterotrophic growth in this cyanobacterium does not appear to involve synthesis of different enzyme forms lacking thioredoxin control sequences.