Rapid Isolation of the 7S-Nerve Growth Factor Complex and Its Subunits from Murine Submaxillary Glands and Saliva

7S-Nerve growth factor (NGF) and its alpha, beta-NGF, and gamma subunits have been purified from murine submaxillary glands and saliva by a combination of gel filtration on rigid polyvinyl gels, reversed-phase liquid chromatography on short alkyl chain supports (C4 columns), and ion-exchange chromatography on silica-based carboxymethyl columns. This technique is superior to previously used methods in that it is much more rapid and allows the purification of larger quantities of polypeptide from the same amount of starting material. Beta-NGF prepared with this method elicits the outgrowth of fibers of cells of a pheochromocytoma cell line (PC 12) in vitro, indicating that the biological activity is not impaired by the organic solvents and strong acids utilized for its isolation.     

A monoclonal antibody which inhibits epidermal growth factor binding has opposite effects on the biological action of epidermal growth factor in different cells

An epidermal growth factor (EGF) receptor-interactive monoclonal antibody (151-IgG) that inhibits EGF binding to PC12 rat pheochromocytoma cells and to various other cell types has been produced. The hybridoma clone was obtained by fusing Sp2/O-Ag14 myeloma cells with splenocytes from Balb/C mice which had been immunized with n-octyl glucoside-solubilized protein from isolated PC12 cell plasma membranes. The antibody is an IgG which binds to protein A. 151-IgG did not bind EGF. At 0.5 degrees C 151-IgG was directly competitive for EGF binding to PC12 cells. It also inhibited EGF binding to bovine corneal endothelial cells, rabbit corneal fibroblasts, human foreskin fibroblasts, and normal rat kidney cells, and it slightly enchanced EGF binding to SW 3T3 cells. PC12 cells have the same number of binding sites for 151-IgG as for EGF (approximately 27,000 sites/cell). 151-IgG inhibited the photoactivatable cross-linking of EGF to a protein of Mr 170,000 in PC12 cells. 151-IgG inhibited the EGF-stimulated incorporation of [3H]thymidine into quiescent bovine corneal endothelial cells, rabbit corneal endothelial cells, epithelial normal rat kidney cells, and SW 3T3 cells while it enhanced the EGF-stimulated [3H]thymidine incorporation into quiescent human foreskin fibroblasts. 151-IgG by itself possessed intrinsic EGF-like activity for human fibroblasts but not for the other cells tested. This suggests that there is a difference in EGF receptors and/or processing in these normal cell types.     

The reaction of alkylating agents with bacteriophage R17. Biological effects of phosphotriester formation

The extent of biological inactivation and of the degradation of the RNA after reaction of bacteriophage R17 with ethyl methanesulphonate, isopropyl methanesulphonate and N-ethyl-N-nitrosourea was studied. Formation of breaks in the RNA chain probably results from hydrolysis of phosphotriesters formed in the alkylation reactions. Near neutral pH the ethyl and isopropyl phosphotriesters are sufficiently stable for the kinetics of the hydrolysis reaction to be followed. Results indicate that the rate of hydrolysis increases rapidly as the pH is raised. The evidence shows that a phosphotriester group does not itself constitute a lethal lesion. The extent of phosphotriester formation by the different agents is discussed in terms of reaction mechanism.     

Synthesis of sulphatide-containing lipoproteins in rat brain

Abstract—

• 1 Puromycin inhibits [¹⁴C]leucine Hincorporation into brain proteins, but has no effect on the incorporation of [³⁵S]sulphate into sulphatide. These effects of puromycin are observed not only with the proteins and sulphatide of whole brain, but also with the protein and sulphatide portion of water-soluble lipoprotein complexes.
• 2 Microsomes can be separated into three subfractions which differ chemically, morphologically and metabolically. Protein synthesis and sulphatide synthesis are located in different submicrosomal fractions.
• 3 The addition of water-soluble brain proteins to the incubation medium causes release of newly synthesized [³⁵S]sulphatide and formation of soluble sulphatide protein complexes. One acceptor protein is identified as the lipoprotein previously shown to bind [³⁵S]sulphatide in vivo (Herschkowitz , Mc Khann , Saxena and Shooter , 1968b).
• 4 These results suggest that protein and sulphatide synthesis can function independently and that association of newly synthesized lipid to preformed protein is possible.

     

Ultracentrifuge studies of histone fractions from calf thymus deoxyribonucleoprotein

Molecular weights and sedimentation coefficients of four major fractions of calf thymus histones were measured. The minimum molecular weights were determined in concentrated solutions of guanidine hydrochloride. The results indicate that, with the possible exception of fraction F3, the fractions are heterogeneous. Comparisons in 0.1m-sodium chloride suggest that fraction F1 does not aggregate and show that fractions F2(a) and F3 aggregate to form larger complexes than does fraction F2(b). The degree of aggregation of each fraction is independent of pH in the range pH1-7. Detailed studies with fraction F2(b) have confirmed that the change in sedimentation coefficient observed as the sodium chloride concentration of the solution is increased results from increases in the apparent molecular weight of the sedimenting units. It has been found that the molecules of fraction F2(b) are present as single molecules only in sodium chloride solutions of 33mm or less. At these low concentrations the effects of charge greatly increase the concentration dependence of the sedimentation rate; the results can, however, be interpreted by using the theory developed by Alexandrowicz & Daniel (1963) and Daniel & Alexandrowicz (1963).     

Mutation of tryptophan-21 in mouse nerve growth factor (NGF) affects binding to the fast NGF receptor but not induction of neurites on PC12 cells.

By using in vitro DNA mutagenesis, we replaced the tryptophan residue at position 21 in mouse nerve growth factor (NGF) with either phenylalanine, leucine or serine. Yield, biological activity, immunological reactivity and receptor binding of the recombinant proteins were determined. All three mutants were produced at considerably lower yields than wild-type NGF, with the serine mutant being undetectable. The results of competitive binding assays show that tryptophan-21 is involved in recognition of the fast NGF receptor of PC12 cells. However, specific biological activity of NGF is not altered by the replacement of tryptophan-21. Our results therefore suggest that biological activity of NGF is not directly coupled to binding to the fast NGF receptor.     

Cell-free synthesis of glial fibrillary acidic protein

Glial fibrillary acidic (GFA) protein has been synthesized in an RNA-dependent cell-free system derived from rabbit reticulocytes. The cell-free synthesized product appears to have the same size as GFA protein isolated from bovine spinal cord, thus showing that GFA protein does not undergo detectable proteolytic processing.     

Does high-mobility-group non-histone protein HMG 1 interact specifically with histone H1 subfractions?

The interaction of the non-histone chromosomal protein HMG (high-mobility group) 1 with histone H1 subfractions was investigated by equilibrium sedimentation and n.m.r. sectroscopy. In contrast with a previous report [Smerdon & Isenberg (1976) Biochemistry 15, 4242--4247], it was found, by using equilibrium-sedimentation analysis, that protein HMG 1 binds to all three histone H1 subfractions CTL1, CTL2, and CTL3, arguing against there being a specific interaction between protein HMG 1 and only two of the subfractions, CTL1 and CTL2. Raising the ionic strength of the solutions prevents binding of protein HMG 1 to total histone H1 and the three subfractions, suggesting that the binding in vitro is simply a non-specific ionic interaction between acidic regions of the non-histone protein and the basic regions of the histone. Protein HMG 1 binds to histone H5 also, supporting this view. The above conclusions are supported by n.m.r. studies of protein HMG 1/histone H1 subfraction mixtures. When the two proteins were mixed, there was little perturbation of the n.m.r. spectra and there was no evidence for specific interaction of protein HMG 1 with any of the subfractions. It therefore remains an open question as to whether protein HMG 1 and histone H1 are complexed together in chromatin.