Structural forms and transitions for the complex of mercury(II) with poly(dG-dC)

Infrared spectroscopy was used to study hydrated double-helical poly(dG-dC) complexed with varying amounts of mercury(II). For one Hg(II) per ten nucleotide residues (r = 0.1), the B structure was stabilized and the B* structure was absent at high hydration. The Z structure did not form as hydration was reduced. For r = 0.2, the B and Z structures coexisted at high hydration and the transition to total Z structure was broad as hydration was reduced. Hg(II) was bound exclusively to the guanine residues probably at N3 or N7 for r less than or equal to 0.25. The cytosine residue did not protonate (at N3) as Hg(II) was bound to guanine. The addition of NaCl together with Hg(II) reduced the binding of Hg(II), stabilized the B structure at the highest hydration and caused a sharp transition between the B and Z structures as hydration was lowered. Hydration with D2O stabilized the Z structure for poly(dG-dC) complexed with HgCl2.     

An active-site peptide from human triose phosphate isomerase

Chloroacetol phosphate totally inactivates human triose phosphate isomerase by the selective modification of a single residue per catalytic subunit. The stability of the protein-reagent bond and the analogies of this active-site modification to those described previously for isomerases from other species indicate that inactivation results from the esterification of an essential glutamyl γ-carboxylate. From peptide maps and their autoradiograms, we conclude that the primary structure adjacent to the glutamyl residue is the same as or similar to that found in triose phosphate isomerases from rabbit and chicken muscle and from yeast.     

Evidence of predatory control of yellow perch (Perca flavescens) recruitment in Lake Erie, U.S.A.

Predation can be a major factor in recruitment success of yellow perch ( Perca flavescens Mitchitl). Trawl catches of age-0 yellow perch in western Lake Erie declined from 870·3 per trawling h in June to 3·3 per trawling h in late July 1988. Coincident with the decline in relative abundance of age-0 yellow perch we found large numbers of age-0 yellow perch in the stomachs of small walleyes ( Stizostedion vitreum Mitchill). From this evidence we hypothesized that predation by walleyes may have caused the demise of the 1988 year-class of yellow perch. We used a population and bioenergetics modelling approach to estimate the impact of walleye predation on the abundance of age-0 yellow perch. Modelling showed that 6·8 × 10⁹ age-0 yellow perch that had attained 18 mm total length ( t.l. ), were eaten by small (age-2 and younger) walleye from June through July 1988. We estimated that walleye ate 28·4–89·7% of the yellow perch reaching 18 mm t.l. during 1988. The majority of this predation (77% of total) was by the abundant age-2 cohort of walleyes. We concluded that, even in a large system such as Lake Erie, predation can play a major role in structuring year-class strength of yellow perch and, thus, management of percid fisheries should be conducted on a fish-community basis.     

Factors influencing distribution of cerebral gas embolism

The results of a series of experiments in baboons centrally cooled to a brain temperature of 18 °C have been described. These studies were characterized by 50% reduction in blood flow to cerebellum after cooling, relative increase in distribution to cerebellar cortex as opposed to white matter, and reduced cerebral oxygen extraction.The physical factors of importance are the viscosity of the blood, chiefly the effect to hematocrit, surface tension, the surface tension coefficient between gas and blood, the radius of the vessel, aud the velocity of the bubble.