Purine mutants of mammalian cell lines. II. Identification of a phosphoribosylpyrophosphate amidotransferase-deficient mutant of Chinese hamster lung cells

A class of purine auxotrophs blocked early in the purine biosynthetic pathway was examined. The inability of these mutants to accumulate formylglycinamide ribotide (FGAR) in the presence of azaserine suggested that one or more of the first three enzymes of the pathway were either missing or defective. By direct enzyme assay, phosphoribosylpyrophosphate (PRPP) amidotransferase (E.C. 2.4.2.14) was found to be absent in extracts of mutant cells. Thus these cells were unable to convert PRPP to phosphoribosylamine (PRA). By reacting ribose 5-phosphate with ammonium ions, PRA was generated nonenzymatically in the incubation mixture, thus enabling us to test for the presence of the two enzymes required to convert PRA to FGAR. It was demonstrated that sufficient amounts of these enzymes, phosphoribosylglycineamide synthetase (E.C. 6.3.1.3) and phosphoribosylglycineamide formyltransferase (E.C. 2.1.2.2), were present in mutant extracts to allow synthesis of FGAR to occur once PRA was so provided.

Thymus-independent antigens: the preparation of covalent, hapten-ficoll conjugates

A general approach is presented for covalently attaching carboxyl and primary amino groups to Ficoll and other high molecular weight polysaccharides in a readily controlled manner. The polysaccharides are omicron-carboxymethylated with chloroacetate in NaOH solutions. Amino groups are next introduced by monoamide formation with ethylenediamine using a water-soluble carbodiimide. Reactions are carried out in aqueous solutions; excess reactants and by-products are removed by dialysis. Three different ways for coupling the 2,4-dinitrophenyl hapten to the amino derivative of Ficoll are described. Preliminary evidence indicates that 2,4-dinitrophenyl-Ficolls, prepared by procedures developed in this study, are potent thymus-independent antigens which can specifically stimulate B cells both in vivo and in vitro. Hapten-Ficoll conjugates should be exceptionally useful for studies of B lymphocyte activation because of the ready availability of the starting material and the ease with which a wide variety of hapten derivatives may be prepared.

Chemotaxis toward sugars in Escherichia coli

Using a quantitative assay for measuring chemotaxis, we tested a variety of sugars and sugar derivatives for their ability to attract Escherichia coli bacteria. The most effective attractants, i.e., those that have thresholds near 10(-5) M or below, are N-acetyl-d-glucosamine, 6-deoxy-d-glucose, d-fructose, d-fucose, 1-d-glycerol-beta-d-galactoside, galactitol, d-galactose, d-glucosamine, d-glucose, alpha-d-glucose-1-phosphate, lactose, maltose, d-mannitol, d-mannose, methyl-beta-d-galactoside, methyl-beta-d-glucoside, d-ribose, d-sorbitol, and trehalose. Lactose, and probably d-glucose-1-phosphate, are attractive only after conversion to the free monosaccharide, while the other attractants do not require breakdown for taxis. Nine different chemoreceptors are involved in detecting these various attractants. They are called the N-acetyl-glucosamine, fructose, galactose, glucose, maltose, mannitol, ribose, sorbitol, and trehalose chemoreceptors; the specificity of each was studied. The chemoreceptors, with the exception of the one for d-glucose, are inducible. The galactose-binding protein serves as the recognition component of the galactose chemoreceptor. E. coli also has osmotically shockable binding activities for maltose and d-ribose, and these appear to serve as the recognition components for the corresponding chemoreceptors.