triphosphatases

Triphosphatases are enzymes that catalyze the hydrolysis of triphosphate groups in substrates containing three phosphate units. In biochemistry, this term is often used for enzymes that act on nucleoside triphosphates (NTPases) or on RNA molecules bearing a 5' triphosphate terminus, but it can also describe enzymes that cleave inorganic triphosphates such as tripolyphosphate.

In RNA biology, RNA 5' triphosphatases remove the gamma phosphate from the 5' end of a nascent transcript, converting a 5'-pppRNA to 5'-ppRNA. This step precedes the addition of the guanine cap by a capping enzyme and is essential for proper mRNA maturation in many eukaryotes and some viruses. These enzymes are often metal-dependent and may utilize distinct catalytic mechanisms across different species. Examples include the Cet1 enzyme in yeast and analogous activities in certain viral capping systems, where the triphosphatase function is integrated into a larger capping complex.

Beyond RNA processing, triphosphatases can refer to enzymes that hydrolyze nucleoside triphosphates (such as ATP or GTP) to their diphosphate forms, releasing inorganic phosphate. Such NTPases participate in energy metabolism, signaling, and various cellular processes, and they occur in diverse structural families with different regulatory features.

In summary, triphosphatases describe a broad class of enzymes that cleave triphosphate linkages, with notable roles in RNA processing as 5' triphosphatases involved in capping, as well as in general nucleotide metabolism through NTP hydrolysis. Their activity contributes to RNA maturation, nucleotide regulation, and cellular energy management.