Structure of a soluble super-active insulin is revealed by the nature of the complex between cyanogen-bromide-activated sepharose and amines

Radioimmunoassay of secretin. A critical review and current status

The radioimmunoassay methods of secretin are reviewed with respect to production of antibody, preparation of radioactive tracers, and effect of plasma interference. The major difference in the secretin assay methods resides in handling plasma interference. Thus the assay sensitivity decreased markedly when the assay was conducted by diluting plasma samples. When the assay was conducted by compensating for plasma interference with homologous hormone-free plasma, the effect of plasma interference was greatly reduced, leading to a more sensitive assay. However, this method probably can not obtain consistent results with plasma samples collected under various experimental conditions. The method is still subject to considerable desensitization and assay variation. On the other hand, the elimination of plasma interference before assay results in the most sensitive secretin assays capable of detecting consistently a significant postprandial rise in plasma secretin level. It is concluded that a sensitive, validated secretin radioimmunoassay should be one that is capable of detecting increments of plasma secretin in response to doses of intraduodenal acid at 0.055 mEq/min or lower and intravenous administration of exogenous secretin at 0.03 CU/kg/hr with concomitant stimulation of pancreatic bicarbonate and water secretion. With a sensitive and accurate radioimmunoassay for secretin, it is now possible to further investigate the physiology and pathophysiology of secretin.

Reagents specific for cell surface components

Mercury, diazonium ions and dyes which bind nucleic acids were covalently linked to dextrans using methods that resulted in non-hydrolyzable reagent-dextran bonds without impairing the binding abilities of the reagents, i.e. these dextran derivatives reacted with thiols, phenols/imidazoles and nucleic acids respectively. Since these dextran derivatives cannot penetrate into cells and since dextran itself does not bind to cells, these compounds represent reagents specific for the cell surface. They may be used both to evaluate cell surface constituents of intact cells and to affect viable cells via an interaction with those constituents. Mercury-dextran was found to bind to cells; the amount of mercury thus attached to the cells was about ten times smaller than when an equivalent concentration of free mercury ions was used. Mercury-dextran, bound to cells after a 30-min exposure at room temperature, was localized on the surface of these cells, as sodium borohydride reduced this complex giving rise to the intact cells, elementary mercury and free dextran which was released into medium. When cells were constantly exposed to the mercury-dextran, its toxic effects were comparable to that of free mercury ions. Diazonium-dextran, which also binds tightly to the cell surface, was also considerably toxic. Dextrans substituted with dyes which bind to nucleic acids were less toxic than the parent dyes themselves; it was shown that the attachment of such a dye to dextran decreased the binding of dye to cells under detection limits.

Enzyme leakage and multipoint attachment of agarose-bound enzyme preparations

The solvolytic detachment of leucine aminopeptidase from Sepharose-enzyme conjugates with multiple and single anchoring bonds has been studied under a variety of conditions by radiochemical and enzymological methods. The release of the single-point-fixed conjugate could be described by a leakage function, derived previously, yielding the first-order rate constant of the cleavage of the enzyme-matrix bond. The nucleophile hydroxylamine increased the detachment rate considerably. The release of the immobilized enzyme was incomplete in all experiments even after prolonged times. The enzyme leakage from multipoint-attached conjugates was still high enough to prohibit a long-term use of such preparations in routine work at room temperature.

A new purification procedure for fumarase based of affinity chromatography. Isolation and characterization of pig-liver fumarase

A new procedure has been developed for the isolation of fumarase (EC 4.2.1.2). It is described for the purification of pigheart and liver enzyme. Pyromellitic acid has been covalently coupled to Sepharose-4B with diaminopropanol as spacer arr. When a dialysed 0.55 saturated ammonium sulphate precipitate is applied to the column, in Tris-acetate buffer, pH 7.3, fumarase remains quantitatively bound. It is eluted by competition, together with a few other proteins, by the natural product L-malate. Malate is removed from the eluate by dialysis. After this highly efficient purification step the enzyme is very easily crystallized. The final yield by 67% for both pig heart and liver preparations. The specific activity of fumarase purified from both tissues is found to be the same. Polyacrylamide gel electrophoresis in dodecylsulphate shows one single band corresponding with a subunit molecular weightof 48500. A single band is also obtained by electrophoresis in acid urea. This new procedure based on biospecific affinity chromatography allows a fast and easy preparation of gram quantities of fumarase.

Biologically active macromolecular forms of oxytocin. [8-Lysine]oxytocin as a suitable ligand

[8-Lysine]oxytocin was synthesized on a solid support and possessed an oxytocic activity of 100 +/- 6 units mumol on the isolated rat uterus. The epsilon-carbamoyl, epsilon-3-carboxypropionyl and epsilon-3-carboxybutryl derivatives were prepared and had uterotonic activities of 400, 55 and 50 units/mumol respectively. [8-Lysine]oxytocin was coupled unambiguously through the epsilon-amino group to the carboxyl groups of carboxymethylated dextrans or epsilon-3-carboxypropionly-gelatin. The macromolecular oxytocins were water-soluble and retained signigicant oxytocic activity. [8-Lysine]oxytocin should prove a useful ligand for affinity chromatography of oxytocin-binding proteins.

Effects of polymer-linked sulfonylurea derivatives on insulin release

In order to elucidate whether polymerlinked sulfonylurea derivatives may serve as tools to locate the sulfonylurea receptor site, an easily detectable sulfonylurea was synthetized and coupled to cyanogen-bromide activated dextran. The conjugate proved to be unstable and to release sufficient amounts of free agent to explain its insulinotropic activity. Based on these findings previous results claiming that dextran-linked sulfonylureas retain biological activity may be questioned. A stable conjugate was obtained when the acrylyl derivative of the sulfonylurea was co-polymerized with acrylamide. Both a high (greater than 50000) and a low (1500) molecular weight fraction of this conjugate failed to stimulate insulin release from the perfused rat pancreas, questioning the ability of macromolecular conjugates to combine with the sulfonylurea receptor site.

Covalent coupling of calf brain prolidase

Calf brain prolidase covalently bound to CNBr-Sepharose 4B, retained about 32% of the activity of the uncoupled enzyme. The free enzyme showed slightly greater stability than the bound preparation when stored at 20 degrees C or at 0 degrees C. However, in either case the free and bound enzymes were more stable at the lower temperature. Greater thermal stability was shown by the free enzyme than by the bound preparation over a temperature range of 25 degrees C-60 degrees C. The free and bound prolidase, with and without Mn+2, had maximal activity at pH 4.0. Although the bound enzyme showed a single maximum, the free preparation exhibited three pH maxima of 4.0, 9.0, and 6.5, in decreasing order of activity. The ions Ag+, Cu+, Hg+2, and Zn+2 were strongly inhibitory on the free enzyme, whereas inhibition of the bound enzyme, with the exception of Zn+2 , was less. Unlike the coupled enzyme, a stimulatory effect was obtained on the free preparation with Co+3, Mg+2, and Mn+2. Various other compounds were studied and their effects were noted.

On the activation of plasma membrane ecto-enzymes by treatment with neuraminidase

It had been proposed that sialyl-residues on the surface of the cell control the activity of certain plasma membrane ecto-enzymes. We have tested the effects of several established (or presumptive) ecto-enzymes in tissue cultures of CNS-derived cells. Application of neuraminidases to cultured mouse neuroblastoma (N-18), neonatal Syrian hamster astrocytes (NN), human astrocytoma (Cox clone) and two lines of primary mouse astroblasts failed to change the activity of ecto-ATPase and 5'-nucleotidase. Only two of the seven neuraminidase preparations produced marked or moderate increases in inorganic pyrophosphatase, p-nitrophenylphosphatase and cholinesterase. We have concluded that the stimulation of these enzymes was not due to removal of sialyl-residues. We suggest that contaminants (haemolysins?) in neuraminidase preparations of Clostridium perfringens increased membrane permeability and facilitated substrate-product translocation.

Complementation of subunits from glycogen phosphorylases of frog and rabbit skeletal muscle and rabbit liver

Activity can be induced in potentially active rabbit skeletal muscle phosphorylase monomers covalently bound to Sepharose by noncovalent interaction with soluble subunits carrying inactive pyridoxal 5'-phosphate analogs or even salicyladlehyde. These analogs are themselves incapable of reconstituting active holophorphorylase from apophosphorylase. Phosphorylases with one intrinsically inactive and one potentially active subunit have about one half of the activity of the native phosphorylase dimer. The usefulness of this technique for subunit complementation was demonstrated by forming hybrid phosphorylases with inactive Sepharose-bound rabbit skeletal muscle subunits containing pyridoxal 5'-phosphate monomethylester and soluble activatable frog muscle and rabbit liver phosphorylase monomers. The inactive Sepharose-bound subunit induced in each case activity in the soluble subunit. But whereas the inactive rabbit muscle phosphorylase subunit even transmitted its characteristic temperature dependence of the rate of the reaction to the frog muscle subunit, it could not propagate its control properties to the liver enzyme. Differences of hybrid phosphorylases are related to immunological and amino acid divergencies among the component enzymes.

Insulin-unresponsive tissues respond to superactive insulin-like material

Insulin-like material prepared from insulin-Sepharose stimulates glucose oxidation by isolated diaphragm of C57Bl/6J ob/ob mice, but insulin does not. This material is much more effective than insulin on epididymal fat tissue from these mice. Insulin-like material and insulin are equipotent on the corresponding tissues from lean littermates.