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INTRODUCTION AND BACKGROUND The concept of the instructional materials center is a relatively new arrival upon the school scene and opinion is divided on the services it should offer, its personnel, and its place in the schools. The basic service idea of the instructional materials center (IMC) is to efficiently and effectively organize materials of all types so that they are readily available to students and faculty. The primary function of the IMC was assumed to be the facilitation of learning by the students. This is a fundamental change from the concept of facilitating teaching by the teachers which the old library and audiovisual center were set up to do. Because of this fundamental change it was necessary to explore new avenues of approach without relying too heavily on the already existing services. That is to say, the improvement of existing services might actually slow down desirable change rather than aid it. For example, the computerization of a retrieval system for books or films might make them more readily available to the teachers and students. But perhaps a better method might be to provide the client with printouts of certain passages in books or to electronically transmit films or videotapes to teachers and students. The term Instructional Materials Center is open to question

Summary A specific method for purification of cross-reacting antibodies from equine anti-pneumococcal sera of types III and VIII has been described. Quantitative studies with mixtures of S3 and S8 have shown that although cross-reacting antibodies isolated from each serum type may be completely precipitated by either polysaccharide alone, the homologous antigen is selectively precipitated from mixtures of the two. An octasaccharide has been isolated from enzymatic digests of S8. Following reduction of the terminal unsaturated hexuronic acid residue with tritium gas, the labeled octasaccharide has been used as a ligand in equilibrium dialysis against type VIII antibodies isolated from horse and rabbit sera. Binding curves show homogeneous affinity at all ligand concentrations.

Using the technique of radioautography, it has been shown that a probable maximum of only 25–50 molecules iodine-125-labeled toxin per cell is bound by human HeLa cells treated with approximately 107 molecules of toxin per cell, or just under one saturating dose. Radioautographs of sections from labeled cells locate most if not all of the toxin molecules fixed to the outer cell membrane. Under identical conditions far less label is taken up by mouse L cells. It is probable that the resistance of this species to diphtheria toxin can be accounted for in terms of the failure of mouse cells to bind the toxin protein. The irreversible inhibition of protein synthesis in a living cell culture by a few molecules of toxin located at the cell surface is discussed in relation to the known interaction between toxin, NAD, and transferase II in mammalian cell extracts.

When diphtheria toxin and NAD are added to soluble fractions containing aminoacyl transfer enzymes isolated from rabbit reticulocytes or from HeLa cells, free nicotinamide is released and, simultaneously, an inactive ADP ribose derivative of transferase II is formed. The reaction is reversible, and in the presence of excess nicotinamide, toxin catalyzes the restoration of aminoacyl transfer activity in intoxicated preparations. In living cultures of HeLa cells, the internal NAD concentration is sufficiently high to account for the rapid conversion, catalyzed by a few toxin molecules located in the cell membrane, of the entire cell content of free transferase II to its inactive ADP ribose derivative. Completely inactive ammonium sulfate fractions containing soluble proteins isolated from cells that have been exposed for several hours to excess toxin, can be reactivated to full aminoacyl transfer activity by addition of nicotinamide together with diphtheria toxin. Transferase II appears to be a highly specific substrate for the toxin-stimulated splitting of NAD and thus far no other protein acceptor for the ADP ribose moiety has been found.