In vitro studies of purine nucleotide biosynthesis in rat intestinal mucosa

The de novo pathway of purine nucleotide biosynthesis in rat intestinal mucosa has been studied using respiring whole cell tissue suspensions and cell-free extracts prepared in isotonic sucrose or buffered saline. The antibiotic azaserine (O-diazoacetyl L-serine) was found to exert an inhibitory effect on the in vitro incorporation of formate-C¹⁴ into the acid-soluble and nucleic acid purines of intact cells when injected intraperitoneally into rats one hour before the animals were sacrificed. Such an inhibition could not be demonstrated if azaserine and a labelled precursor were added to incubation vessels simultaneously with tissue suspensions prepared from normal animals. This indicated that azaserine had to be in contact with a tissue constituent for a period of time before the enzymes concerned were affected. Studies with cell-free extracts of mucosal tissue showed that glycine-l-C¹⁴ could be metabolized in small amounts to a form which displayed some of the properties of glycinamide ribotide, a known intermediate in the de novo synthesis of inosinic acid by pigeon liver enzymes. Because azaserine does affect de novo synthesis of purines and because isotopic glycine is transformed to a form having properties in common with those reported for glycinamide ribotide, it appears possible that the enzymatic steps of purine synthesis in mucosal tissue are similar to those already known for pigeon liver. The level of free glycine in mucosal tissue has been measured by a method not previously employed. The results obtained are intermediate in value to those of the two groups who have studied the problem independently. An average value of 0.425 mg. free glycine per gram (fresh weight) of mucosal tissue was obtained.Medicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat