A general method for the detection and quantitation of antigens in solubilized cells using radiolabeled fab fragment

which, if suitable for centrifugation, are not suitable for other biochemical manipulations. This necessitates switching to centrifuge tubes for the centrifugation steps and back again, involving unnecessary delay. Many commercial makes of tubes may be adapted for centrifugation if a suitable adapter can be found. This paper describes a quick and economical method for making custom-made adapters which are suitable for the numerous low-speed centrifugation tasks required for biochemical techniques. Materials and methods. The adapters were made for a colleague who required sucrose step gradients to be set up in numerous plastic centrifuge tubes. These tubes were of an unknown make but were required to fit into a Hettich universal benchtop centrifuge (Hettich Zentrifugen, D-7200 Tuttlingen, Germany) fitt.ed with four swing-out buckets. The material used was silicone rubber 3120RTV red (Dow Corning Corp., Midland, MI). This comes supplied in a l-lb tin together with a catalyst (S standard curve). The insides of the swing-out buckets were covered with a rolled layer of transparent acetate film to allow some clearance. To add air channels, V-shaped struts may be lightly tacked into place onto the transparent film. Uhu adhesive or Cow gum is suitable for these temporary joints. The silicone rubber was thoroughly mixed with the catalyst at a ratio of lO:l, using a wooden spatula, and poured into the buckets to a predetermined height, allowing for displacement of some of the silicone rubber by the cent,rifuge tubes. Because numerous centrifuge tubes were required, it was decided to fit three tubes into one bucket. These tubes were taped together and inserted into the silicone rubber. The buckets were placed close to each other. A glass plate with a weight was placed on top of the centrifuge tubes to align and keep