Studies of activating and nonactivating metal ion binding to yeast enolase

Measurements of binding of certain divalent cations to yeast apoenolase were made using a pH-meter, chromatography, a divalent cation electrode, and ultrafiltration. The binding of the activating metal ions Mg2+ and Co2+ and the nonactivator Ca2+ were studied as functions of the presence or absence of substrate/product, phosphate, and fluoride or level of Tb3+. The data suggest phosphate and fluoride increase Mg2+ binding but not Ca2+ binding. Substrate/product appears to increase Ca2+ binding as well as that of Mg2+ and Co2+. In the presence of substrate, Co2+ binding was 5-6 mol/mol dimer. In the absence of substrate/product, Tb3+ reduced Co2+ binding from 4 mol/mol to 2. These data are interpreted in terms of binding to "conformational," "catalytic" (substrate/product dependent), and "inhibitory" sites. Measurements of Tb3+ fluorescence quenching by Co2+ suggested that the distance between "conformational" sites on the two subunits was large, while the distance between "conformational" and "inhibitory" sites was ca. 17 +/- 4 A. Potentiometric titrations of apoenzyme with Ca2+ and Mg2+ showed that the metal ions produced the same proton release in the presence or absence of substrate/product. If phosphate and fluoride were present, then more protons were released if Ca2+ was the titrant rather than Mg2+, suggesting a difference in ionization state in the complex with the activating metal. Electron paramagnetic resonance studies of Co2+ binding to the various sites in the enzyme are presented. The Co2+ bound to all three sites appears to be high spin, consistent with a preponderance of oxyligands in an octahedral environment. Substrate, citrate, and a strongly binding substrate analogue strongly enhance the hyperfine structure of conformational Co2+. This is interpreted as the result of a change in interaction of an axial ligand to conformational Co2+ produced by carbon-3 of substrate or analogue.     

LARGE-SCALE ISOLATION AND FRACTIONATION OF ORGANS OF DROSOPHILA MELANOGASTER LARVAE

Methods for the mass isolation of diverse organs from small animals are described. They involve novel devices: a mechanical dissecting system, a centrifugal agitator for the separation of fibrillar from globular particles, and a settling chamber for the fractionation at unit gravity of particles with sedimentation velocities above the useful range for centrifugation. The application of these methods to the isolation of polytene and nonpolytene nuclei from Drosophila melanogaster larvae is described.     

An affinity column for renin

An affinity column for renin was prepared making use of the strong affinity of pepstatin for renin. Pepstatin is an N-acylated pentapeptide from $\text{Actinomycetes}$ with the following structure: isovaleryl-L-valyl-L-valyl-4-amino-3-hydroxy-6-methylheptanoyl-L-alanyl-4-amino-3-hydroxy-6-methylheptanoic acid. This peptide was coupled to aminoethylated polyacrylamide gel either directly with the water-soluble carbodiimide, 1-ethyl-3-(dimethylaminopropyl) carbodiimide, or through the N-hydroxy succinimide ester. Submaxillary renin was selectively retained by a small column of the gel and was eluted by a salt gradient to produce a highly pure material. This column was also effective for the purification of renal renin.