(1) Four main species of rapidly synthesised trichloroacetic acid-insoluble derivatives of adenylate can be separated in extracts from rat hearts. (2) The major species, accounting for more than 70% of the total, is phosphoglyceroyl-ATP; two others (16% of the total) are closely related to it. (3) Around 10% of incorporated radioactivity is in a high-molecular-weight form with a phosphate/purine ratio of 0.8; comparison of [14C]uridylate and [14C]adenylate incorporation supports the suggestion that this is a rapidly synthesised species of RNA which represents about 4% of total RNA in heart. (4) Values are given for the contents of UTP, UDP and UDPglucose in adult rat hearts.
