One batch of isolated, purified mitochondria was placed into a pH 7.2 solution. Another batch of identical mitochondria was placed into a pH 3.2 solution. The rates of electron transport in the two batches were measured. At pH 7.2 the rate was normal, but at pH 3.2 electron transport had stopped completely. In fact, it was seen that small amounts of NADH were synthesized from NAD+ in the pH 3.2 solution. Explain how synthesis of NADH could happen under these conditions.