Biosynthetic Methods Research Articles

Some experience with labeling sugars by tritium gas exposure.

Our interest in the Wilzbach direct tritium-labeling procedure [1] was aroused by the possibilities it offered to obtain radioactive counterparts of sugars and sugar analogs for which chemical synthesis from C14-labeled precursors is either very difficult, prohibitively expensive, or both. With few exceptions, it seems, only naturally occurring hexoses are easily labeled with C14, inasmuch as biosynthetic methods may be used. In our older studies with animal tissue hexokinase [2], and in our more recent studies of various aspects of membrane transport of sugars in ascites tumor cells [3], kidney cortex slices [4] and intestinal epithelial cells [5, 6] we have found particularly useful a group of compounds which are analogs of D-glucose but which, unlike glucose, cannot be metabolized by animal tissues. It is this very property, metabolic inertness, so useful to us on the one hand, that is, on the other hand, an effective barrier to easy C14-labeling of these compounds.

Studies with insulin labelled with iodine-131.

Recently there has been considerable interest in proteins labelled with iodine 131 in the tyrosine of the protein molecule. Much of this work has been concerned with plasma proteins such as albumin and γ-globulin with the result that there is now wide experience of the behaviour of these labelled protein molecules. It is accepted that iodination at a level of not more than one atom of iodine per molecule has very little effect on the chemical and biological properties of the protein, whilst iodination above this level results in considerable changes in these properties (McFarlane, 1956). Interest in proteins labelled with iodine 131 has been extended to include hormones with a protein structure, such as A.C.T.H. and insulin; a number of reports have appeared describing experimental work involving the use of an 131I label for both of these hormones. An account of the preparation of 131I-labelled insulin was published as long ago as 1943 by Reiner, Lang, Irvine, Peacock and Evans who were interested in measuring differences in the rate of absorption of various types of insulin. Biosynthetic methods for the production of insulin labelled with 14C or 35S have been described by Light and Simpson (1956). These workers incubated slices of pancreas in a medium containing 14C-leucine, or 35S-methionine. However, the techniques used are highly specialised and yields of the labelled insulin are poor. The biosynthetic method has recently been repeated by Duncomb and Pain (1959) using tritium-labelled leucine, with very much better results.

A Description of Penicillin

THE unique biological properties of penicillin, as shown by its high toxicity to certain bacteria and tolerance by the mammalian organism, gave such promise of medical value that an unprecedented effort was made to work out the chemical constitution of penicillin in order to devise methods of chemical synthesis which could be used on a commercial scale. The objective which provided the impetus to the research has not been achieved, however, and it is not likely that the present biosynthetic methods will be superseded by chemical methods in the near future. The Chemistry of Penicillin Report on a Collaborative Investigation by American and British Chemists under the joint sponsorship of the Office of Scientific Research and Development, Washington, D.C., and the Medical Research Council, London. Compiled under the auspices of the National Academy of Sciences, Washington, D.C., pursuant to a Contract with the Office of Scientific Research and Development. Editorial Board: Hans T. Clarke John R. Johnson Sir Robert Robinson. Pp. x + 1094. (Princeton, N.J.: Princeton University Press; London: Oxford University Press, 1949.) £9 9s. net.