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The electrophoretic behaviour of oligodeoxynucleotides on ion-exchange papers was studied systematically with particular attention to applications in sequence analysis. Complex mixtures of larger oligonucleotides were fractionated by electrophoresis on cellulose acetate followed by t.l.c. on polyethyleneimine-cellulose. The behaviour of the oligonucleotides on polyethyleneimine-cellulose and on the two-dimensional system can provide a useful guide to their sequence. Detailed results from some of these experiments have been deposited as Supplementary Publication SUP 50031 (13 pages) at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1973), 131, 5.

Dimensionless apparent ionization constants of charged low-molecular-weight species may be obtained from paper-electrophoretic data at 20-25 degrees C with buffers (I0.1-0.5) of measured pH (1.5-12.5) containing oxalate ions. Relative mobilities rather than absolute mobilities were measured by using glycerol and m-nitrobenzenesulphonate respectively as standards of zero and unit mobility. Application of the procedure to ionizations of adenine, adenosine, 2′-deoxyadenosine, 3′-deoxyadenosine, 3′:5′-cyclic AMP, ADP, ADP-glucose-agrocin 84 and ATP is described.

RESP-3032

1. A new method is described for f∈≥rpr∫∈g'cysteicaceptsderivedomthedisϕ––debrsofprote∈s.Cyst∈epeptsareseparatedbypapere≤ctrophoresisand⊗zedonpaperbyperformicacapour.E≤ctrophoresisatright∠s→thefirstdirection∏ucesparal≤lgroupsofcysteicaceptsly∈goffadiagonal.Thisf∈≥rpr∫∈g′cysteicaceptsderivedomthedisϕdebrsofprote∈s.Cyst∈epeptsareseparatedbypapere≤ctrophoresisand⊗zedonpaperbyperformicacapour.E≤ctrophoresisatright∠s→thefirstdirection∏ucesparal≤lgroupsofcysteicaceptsly∈goffadiagonal.Thisfingerprint' reveals the way in which the cysteic acid peptides were originally joined in the protein. 2. The method allows a very easy selective purification of cysteic acid peptides. 3. By applying this method to bovine chymotrypsinogen A, we found that the half-cystine residues were linked 1–122, 42–58, 136–201, 168–182 and 191–220.

A modified procedure for the separation of oligoribonucleotides is described that is based on the combination of t.l.c. on cellulose and electrophoresis on DEAE-paper at 4000 V on a cooling plate. The technique is relatively rapid and allows the analysis of larger quantities than is possible by electrophoresis on cellulose acetate.

The Medical Research Council Medicinal Plants Survey in its expedition to Africa collected many specimens of the seed of Strophanthus hi8pidus P.DC. and S. sarmento8us P.DC., mostly from individual plants, in order to investigate the occurrence of sarmentogenin, a substance which forms a possible starting material for the production of cortisone. The isolation of sarmentogenin from certain of these seeds has already been reported (Callow, Meikle & Taylor, 1951). The present paper is a report on the preliminary investigation ofall the samples collected, and reveals certain interesting features about the distribution of cardiac aglycones in various Strophanthus species. As the examination of each seed sample by isolation of the constituents might take several years for completion, a method has been developed for the routine semi-micro investigation of the easily hydrolysable glycosides of the seeds. These easily hydrolysable glycosides (Reichstein, 1951), which are completely hydrolysed by refluxing for half an hour in 50% aqueous methanol which has been made 0-1N with respect to sulphuric acid, are those in which the steroidal portion of the molecule is directly attached in a glycosidic linkage to a 2deoxy sugar. Most of the best known glycosides belong to this group, which is much easier to investigate than the group in which the aglycones are directly attached to 'normal' sugars carrying a hydroxyl group at C(2), such as glucose or rhamnose, where isolation of the intact aglycone is usually difficult and has in several cases not yet been achieved. Investigation of the 'normal' glycosides in our seed samples has so far only been carried out in selected cases. The paper-chromatographic method of Zaffaroni, Burton & Keutmann (1950) (cf. Burton, Zaffaroni & Keutmann,1951)hasbeenusedbySchindler & Reichstein (1951) for separating this type of substance, but the procedure is in many ways complicated

1. A diagonal electrophoretic technique for studying the amino acid sequence around cysteine and cystine residues in proteins is described. The residues are first converted into S-aminoethylcysteine, and the protein is then treated with S-ethyl trifluorothioacetate, which trifluoroacetylates all the protein amino groups. The modified protein is digested enzymically and the resulting peptides are separated by paper electrophoresis. After exposure of the peptides on the paper to ammonia vapour, the electrophoresis is repeated, this time at right angles to the original direction. Peptides from which a trifluoroacetyl group is removed by the ammonia treatment will vacate the 45° diagonal formed by all other unaffected peptides owing to the exposure of an additional amino group and consequent increased electrophoretic mobility towards the cathode. Peptides containing lysine or S-aminoethylcysteine are readily purified by this technique. 2. The successful application of the technique to bovine insulin is described. 3. Various methods for distinguishing peptides containing lysine from those containing S-aminoethylcysteine in more complicated proteins are suggested and discussed.