7 research outputs found
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
We systematically surveyed period variations of superhumps in SU UMa-type
dwarf novae based on newly obtained data and past publications. In many
systems, the evolution of superhump period are found to be composed of three
distinct stages: early evolutionary stage with a longer superhump period,
middle stage with systematically varying periods, final stage with a shorter,
stable superhump period. During the middle stage, many systems with superhump
periods less than 0.08 d show positive period derivatives. Contrary to the
earlier claim, we found no clear evidence for variation of period derivatives
between superoutburst of the same object. We present an interpretation that the
lengthening of the superhump period is a result of outward propagation of the
eccentricity wave and is limited by the radius near the tidal truncation. We
interpret that late stage superhumps are rejuvenized excitation of 3:1
resonance when the superhumps in the outer disk is effectively quenched. Many
of WZ Sge-type dwarf novae showed long-enduring superhumps during the
post-superoutburst stage having periods longer than those during the main
superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to
be strongly correlated with the fractional superhump excess, or consequently,
mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with
multiple rebrightenings tend to have smaller period derivatives and are
excellent candidate for the systems around or after the period minimum of
evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte
Identification of a GH110 Subfamily of α1,3-Galactosidases: NOVEL ENZYMES FOR REMOVAL OF THE α3GAL XENOTRANSPLANTATION ANTIGEN*S⃞
In search of α-galactosidases with improved kinetic properties for
removal of the immunodominant α1,3-linked galactose residues of blood
group B antigens, we recently identified a novel prokaryotic family of
α-galactosidases (CAZy GH110) with highly restricted substrate
specificity and neutral pH optimum (Liu, Q. P., Sulzenbacher, G., Yuan, H.,
Bennett, E. P., Pietz, G., Saunders, K., Spence, J., Nudelman, E., Levery, S.
B., White, T., Neveu, J. M., Lane, W. S., Bourne, Y., Olsson, M. L.,
Henrissat, B., and Clausen, H. (2007) Nat. Biotechnol. 25,
454–464). One member of this family from Bacteroides fragilis
had exquisite substrate specificity for the branched blood group B structure
Galα1–3(Fucα1–2)Gal, whereas linear oligosaccharides
terminated by α1,3-linked galactose such as the immunodominant
xenotransplantation epitope Galα1–3Galβ1–4GlcNAc did
not serve as substrates. Here we demonstrate the existence of two distinct
subfamilies of GH110 in B. fragilis and thetaiotaomicron
strains. Members of one subfamily have exclusive specificity for the branched
blood group B structures, whereas members of a newly identified subfamily
represent linkage specific α1,3-galactosidases that act equally well on
both branched blood group B and linear α1,3Gal structures. We determined
by one-dimensional 1H NMR spectroscopy that GH110 enzymes function
with an inverting mechanism, which is in striking contrast to all other known
α-galactosidases that use a retaining mechanism. The novel GH110
subfamily offers enzymes with highly improved performance in enzymatic removal
of the immunodominant α3Gal xenotransplantation epitope
Bacterial glycosidases for the production of universal red blood cells
Enzymatic removal of blood group ABO antigens to develop universal red blood cells ( RBCs) was a pioneering vision originally proposed more than 25 years ago. Although the feasibility of this approach was demonstrated in clinical trials for group B RBCs, a major obstacle in translating this technology to clinical practice has been the lack of efficient glycosidase enzymes. Here we report two bacterial glycosidase gene families that provide enzymes capable of efficient removal of A and B antigens at neutral pH with low consumption of recombinant enzymes. The crystal structure of a member of the alpha-N-acetylgalactosaminidase family reveals an unusual catalytic mechanism involving NAD(+). The enzymatic conversion processes we describe hold promise for achieving the goal of producing universal RBCs, which would improve the blood supply while enhancing the safety of clinical transfusions