Possibilities of enzymic synthesis of nucleoside-.5'-triphosphates- 14CC(U) of adenine, guanine, cytosine and uracil of high spec@ activity and radiochemical purity by means of a purijied enzyme isolatedfrom Escherichia coli B were studied. The efect of enzyme concentration in the reaction mixture in dependence on the time of the enzyme reaction is decisive for an optimal production of radioactive nucleoside-5'-triphosphates. A simple and rapid method of preparation of radioactive nucleoside-5'-triphosphates, including preparative paper chromatography as the single isolation step, is described and information on the radiolysis of the isolated nucleotides is presented.INTRODUCTION.

An excellent communication dealing with the enzymatic preparation of deoxyribonu‐. cleosides labelled with 14C in the base, using a crude enzyme extract of Lactobacillus helveticus has been published in this Journal (1) quite recently by Cardinaud and Viswanthan. The most important result was a high degree of conversion of pyrimidine bases to the corresponding deoxyribosides. In connection with this work we wish to present some observations from the same field made in our Laboratory (2). It was the purpose of our work to isolate the enzyme trans‐N‐deoxyribosylase from a Lactobacillus helveticus culture grown just in sterile milk without any additives, to test the enzymatic activity of the isolated enzyme and its suitability for rapid enzymatic synthesis of deoxyribonucleosides labelled with radiocarbon 14C.