Gram scale purification and preparation of rabbit liver zinc metallothionein.

A simplified procedure for purifying gram quantities of rabbit liver metallothionein (MT) using gel filtration and anion exchange chromatography is presented. The MT purification made use of anion exchange batch elution chromatography which greatly shortened the procedure. Quantitation techniques for use with crude and purified MT are discussed. This paper also describes the preparation of large amounts of ZnMT from Cd,ZnMT.

Conjugation of a monoclonal antibody with a DTPA modified random copolymer of hydroxyethyl methylacrylate and methyl methacrylate.

A new approach for covalent coupling diethylenetriaminepentaacetic acid (DTPA) molecules to a partially reduced monoclonal antibody utilizes a malemide modified copolymer of hydroxyethyl methylacrylate and methyl methacrylate (DTPA copolymer) prepared by the group transfer polymerization (GTP) method. An average of 6 DTPA molecules were incorporated per mol maleimeide DTPA copolymer and 1.5 mol maleimide DTPA copolymer per mol antibody. Maleimide DTPA copolymer modified antibody was intramolecularly cross-linked, reduced immunoactivity and had a high in vivo liver uptake.

Site-directed chemical modification and cross-linking of a monoclonal antibody using equilibrium transfer alkylating cross-link reagents.

A new, more reactive group of protein cross-linkers in the class of equilibrium transfer alkylating cross-link (ETAC) reagents has been synthesized. These compounds include alpha,alpha-bis[(p-chlorophenyl)methyl]- and alpha,alpha-bis[(p-tolylsulfonyl)methyl]acetophenones substituted in the acetophenone ring with chloro, nitro, amino, and carboxyl groups and derivatives. Included are an 125I-labeled ETAC reagent and a 111In-labeled DTPA (diethylenetriaminepentaacetic acid) ETAC for site direction and biodistribution studies. These ETAC compounds were reacted with unreduced and partially reduced antibody under mild pH (pH 4-8) and room temperature conditions to give cross-linked structures. Examination of resultant cross-linked antibody via size-exclusion HPLC, sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis, and an enzyme linked immunosorbent assay revealed that (1) both interantibody as well as intraantibody cross-linking had occurred; (2) the level of inter- and intraantibody cross-linking varied with the substituent on the ETAC; (3) the stability of the cross-links on the reducing SDS gels varied with substituents on the ETAC; (4) little if any immunoreactivity was lost after reaction with one of the more effective ETAC cross-linking compounds; (5) the 125I-labeled ETAC sulfhydryl cross-linking in partially reduced antibody increased with pH whereas amine cross-linking with the unreduced antibody decreased with pH; (6) the optimum pH for sulfhydryl site direction was pH 5.0; (7) the 111In DTPA ETAC labeled antibody had a biodistribution in CD1 mice similar to that of the 111In bis cyclic anhydride DTPA labeled antibody.

Heterobifunctional cross-linking of a monoclonal antibody with 2-methyl-N1-benzenesulfonyl-N4-bromoacetylquinonediimide.

The Cyssor reagent, 2-methyl-N1-benzenesulfonyl-N4-bromoacetylquinonediimide, which will cleave a protein chain at Cys under acidic conditions, cross-linked unreduced and partially reduced antibody at pH 8.0. No cleavage of the antibody occurred suggesting that the Cyssor reagent may be useful with certain proteins as a heterobifunctional cross-linker.

Pharmacokinetics of the monoclonal antibody B72.3 and its fragments labeled with either 125I or 111In.

A comparison of the pharmacokinetics of intact B72.3 (a murine monoclonal antibody specific for human breast and colon carcinoma) with F(ab')2 and Fab fragments labeled with 111In and 125I was done in athymic mice bearing target (LS174T) and non-target (HCT-15) tumors. IgG B72.3 labeled with either isotype imaged LS174T. Biodistributions of both labels were similar in all organs except liver. F(ab')2 also imaged the LS174T tumor, while Fab bearing either isotype did not. The blood clearance was Fab greater than F(ab')2 greater than immunoglobulin G B72.3 for both isotopes. 111In-labeled fragments yielded large accumulations in the kidneys which persisted for 2 days. The different patterns of biodistribution for the various forms of B72.3 labeled with the two isotopes suggest that the most desirable combination of fragment and isotope will depend on the intended use.

An alternative model for the binding and release of diferric transferrin by reticulocytes.

The biphasic binding of diferric transferrin to reticulocytes has been reevaluated with a series of kinetic and equilibrium studies. Identical binding progress profiles were observed for reticulocytes in the presence or absence of oxygen. The relative size of the rapid initial adsorption step could be increased to ca. 65% of the total binding by stripping the cells of endogenous transferrin or reduced to 0% by preloading the cells with nonradiolabeled diferric transferrin. Preloading the cells with 125I-labeled diferric transferrin and chasing with 131I-labeled diferric transferrin revealed identical rate constants for release and binding. Scatchard plots of equilibrium binding of diferric transferrin to reticulocytes showed no significant effects of anaerobiasis or 2,4-dinitrophenol on the equilibrium binding constant or the maximum number of binding sites. The potent microtubule inhibitor nocodazole had no effect on the progress curves for transferrin binding or iron uptake by reticulocytes. It was concluded that the rapid adsorption step in the binding profile represents binding to open receptors and that the slow first-order binding phase represents binding of radiolabeled transferrin to receptors already occupied by nonlabeled endogenous transferrin as this endogenous transferrin leaves the receptors. Furthermore, this first-order binding phase, unlike iron uptake, does not require the presence of active oxidative phosphorylation. These findings are consistent with a specific desorption-adsorption model for the interaction of diferric transferrin with reticulocytes.

Specific membrane receptors for diferric-transferrin in cultured rat skeletal myocytes and chick-embryo cardiac myocytes.

A classical approach was used to determine whether myocyte cultures exhibited diferric-transferrin binding phenomena consistent with the presence of specific, high-affinity membrane receptors. Experiments were performed using a continuous cell line, designated L-6, derived from rat skeletal muscle, as well as primary cultures of chick-embryo cardiac myocytes. Rat transferrin isolated from pooled serum was used in experiments involving L-6 cells, and ovotransferrin isolated from hen's egg white was used with the chick-embryo cardiac myocytes. The data from equilibrium binding experiments, corrected for nonspecific binding, and analyzed by Scatchard analysis indicated that there were approximately 2 x 10(5) transferrin receptors per L-6 myocyte and 2 x 10(4) ovotransferrin receptors per cardiac myocyte present, under the conditions used for the equilibrium binding experiments. Whereas the L-6 myocytes grew exponentially under the assay conditions, the cardiac-myocyte cultures were in a non-dividing state. It is thought that the differences in receptor number per cell reflect changes arising form the differing ion demand made by the cells, under these two growth conditions. It is clear that myocytes acquire iron from diferric (ovo)transferrin in a process that involves high-affinity, specific binding to membrane receptors.