LACS cell separator

The LACS cell separator is marketed by Medilog (Appendix 3). This simply consists of a separating chamber on which a 360 ml Ficoll gradient (2.5-7.5%) is made and a cell suspension is layered onto the gradient through a sieve. 

Fig. 11.3.3. HPLC separation of glycolipids from human erythrocytes. Chromatographic conditions column, stainless steel tube (5000 x 2.1 nun) packed with a pellicular silica gel packing with an average particle size of 27 /im mobile phase, 10 min gradient of 2-17% aqueous ethyl acetate in hexane flow rate, 2 ml/min detection, UV at 280 nm. The red blood cell neutral glycolipids were isolated from 5 ml of normal blood. Peaks 1, Glc-Cer 2, Lac-Cer 3, Gal-Lac-Cer 4, globoside. Reproduced from Ullman and McQuer (1977), with permission.

The operator of the lac operon in E. coli (Fig. 94) is composed of four sites — each of them five nucleotides in length — which are separated by one-two nucleotide spacers. The synthesis of repressor proteins is controlled by a special gene known as the regulator (i). The protein repressor for each operator is constantly being synthesized, but at a very low rate. No more than 10-20 molecules are present in the cell at any time. The attachment of the activated operon protein (CAP), which is an acceptor of cAMP, and the removal of repressor protein from the DNA of the operator under the control of substrate (lactose) concentration, are both necessary for the initiation of transcription. Cyclic AMP does not associate with the activator (CAP) if its concentration is low in the cell. Hence, the operon remains in the repressed state (Blattner and Dahlberg, 1972 Blattner et al., 1972 Khesin, 1972 Bresler, J973). The termination of transcription is also determined by a special site on the DNA. 

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