Population movement and city-suburb redistribution: an analytic framework.

This paper introduces an analytic framework that can be used to assess the relationships between individual movement differentials and place characteristics, on the one hand, and aggregate mobility levels and city-suburb population change (in size or composition), on the other. Application of this framework using census data for individual metropolitan areas allows the analyst to decompose population changes due to net migration into contributing mobility streams and their component rates which are subject to unique community and individual influences. The paper provides both theoretical and empirical rationale for the framework, illustrates its use with 1970 census data, and discusses its implications for empirical research on city-suburb population redistribution.

Isotope-tapping experiments with rabbit liver fructose bisphosphatase.

Isotope-trapping experiments with mental-free rabbit liver fructose 1,6-bisphosphatase have shown that enzyme-bound D-fructose 1,6-bisphosphate completely dissociates prior to enzyme turnover initiated by Mn2+ as the catalytic metal. The exchange rate of the binary enzyme-D-fructose 1,6-bisphosphate complex with the substrate pool is, therefore, more rapid than its conversion to products, suggesting that structural Mn2+ is necessary for productive substarate binding. Rapid-quench isotope-trapping experiments confirm the requirement for structural Mn2+ ions for productive binding to occur.

Substrate form of D-frutose 1,6-bisphosphate utilized by fructose 1,6-bisphosphatase.

Rapid quench kinetic experiments on fructose 1,6-bisphosphatase demonstrate a stereospecificity for the alpha anomer of fructose 1,6-bisphosphate relative to the beta configuration. The beta anomer is only utilized after mutarotation to the alpha form in a process that is not enzyme catalyzed. Studies employing analogues of the acyclic keto configuration indicate that the keto form is utilized at a rate less than 5% that of the alpha anomer, a finding also confirmed by computer simulation of the rapid quench data.

Stimulation of human platelet guanylate cyclase by fatty acids.

Guanylate cyclase from human platelets was over 90% soluble, even when assayed in the presence of Triton X-100. A time-dependent increase in activity occurred when the enzyme was incubated at 37 degrees and this spontaneous activation was prevented by dithiothreitol. Arachidonic acid stimulated the soluble enzyme activity approximately 2- to 3-fold.

Binding of acetyl-CoA to chicken liver pyruvate carboxylase.

Pyruvate carboxylase from chicken liver is a tetramer whose catalytic activity is completely dependent on the presence of acetyl-CoA. However, no direct evidence concerning the nature of the binding of the activator to the enzyme has been available. This is due in part to the instability of the enzyme and its ability to hydrolyze acetyl-CoA at an appreciable rate.

Structural properties of pyruvate carboxylases from chicken liver and other sources.

Varieties of pyruvate carboxylase [pyruvate: CO2 ligase (ADP-forming), EC 6.4.1.

Kinetic and binding studies of Mn (II) and fructose 1,6-bisphosphate with rabbit liver hexosebisphosphatase.

The separate interaction of the substrate fructose 1,6-bisphosphate and a metal ion cofactor Mn2+ with neutral hexosebisphosphatase has been studied under equilibrium conditions at pH 7.5 with gel filtration and electron paramagnetic resonance measurements, respectively. Binding data for both ligands to the enzyme yielded nonlinear Scatchard plots that analyze in terms of four negatively cooperative binding sites per enzyme tetramer.

Chronic binodal block with Wenckebach phenomenon.

Coexistent sino-atrial and atrioventricular block with Wenckebach phenomenon is an extremely unusual cardiac arrhythmia. Observations on the natural history of sinus node dysfunction are rare. For over six years our elderly patient has been followed without symptoms but with increasing severity of atrio-ventricular block.