Glycolysis is turned off when ATP is present in adequate amounts, because ATP is an ............. phosphofructokinase enzyme involved in one of the early steps of the pathway.

Explanation

**Step-by-Step Solution:**

1. **Understanding Glycolysis**: Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing ATP and NADH in the process. It consists of several steps, and one of the key enzymes involved is phosphofructokinase (PFK).

2. **Role of ATP in Glycolysis**: ATP is the energy currency of the cell. When the levels of ATP are high, it indicates that the cell has sufficient energy available.

3. **Regulation of Phosphofructokinase**: Phosphofructokinase is a crucial regulatory enzyme in glycolysis. Its activity is influenced by the concentration of ATP.

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