Malonate is a competitive inhibitor of succinic dehydrogenase, which is an enzyme involved in the citric acid cycle. Malonate is structurally similar to succinate, the natural substrate of succinic dehydrogenase. Therefore, malonate can bind to the active site of the enzyme and prevent succinate from binding, which inhibits the enzyme's activity. This leads to a decrease in the production of ATP, which can have a negative impact on cellular respiration.