Inorganic pyrophosphatase (PPase) is a ubiquitous enzyme found in all living organisms, from bacteria to humans. It plays a central role in cellular metabolism by catalyzing the hydrolysis of inorganic pyrophosphate (PPi), a byproduct of numerous biochemical reactions, into two molecules of orthophosphate (Pi). This enzymatic reaction is thermodynamically favorable and helps drive various biosynthetic pathways by preventing the accumulation of PPi, which can inhibit essential metabolic processes. The catalytic mechanism of inorganic pyrophosphatase involves a two-step hydrolysis reaction. In the first step, a metal ion within the active site coordinates with the pyrophosphate substrate, facilitating the nucleophilic attack by a water molecule. This results in the formation of a phosphorylated enzyme intermediate. In the second step, a second water molecule hydrolyzes this intermediate, leading to the release of two molecules of orthophosphate. The metal ion cofactor plays a crucial role in stabilizing the transition state and enhancing the efficiency of the catalytic reaction. Inorganic pyrophosphatase activity is regulated at multiple levels to maintain cellular homeostasis. Expression of the enzyme is tightly regulated in response to metabolic demands and environmental stimuli. Additionally, post-translational modifications, allosteric regulation, and interactions with other proteins can modulate its activity. Next to its role in nucleotide biosynthesis, inorganic pyrophosphatase participates in energy metabolism pathways such as glycolysis and oxidative phosphorylation. By catalyzing the hydrolysis of PPi, inorganic pyrophosphatase helps maintain the balance of phosphate ions within cells, which is crucial for DNA replication, RNA transcription, and protein synthesis.
