32 有關甘油-3-磷酸穿梭路徑（glycerol 3-phosphate shuttle）之敘述，下列何者正確？

 此穿梭路徑將細胞質的NADH穿過粒線體內膜運送至間質（matrix）而得到3ATP / NADH

此穿梭路徑可將細胞質的NADH轉換為NAD+，同時在粒線體生成FADH2

此穿梭路徑不需要粒線體甘油-3-磷酸脫氫酶（mitochondrial glycerol 3-phosphate dehydrogenase）的參與

此穿梭路徑需要蘋果酸脫氫酶（malate dehydrogenase）的參與

B

The glycerol-3-phosphate shuttle is a mechanism that regenerates NAD+ fromNADH, a by-product of glycolysis. Its importance in transporting reducing equivalents is secondary to the malate-aspartate shuttle.

Reaction

In this shuttle, the enzyme called cytoplasmic glycerol-3-phosphate dehydrogenase(GPD) converts dihydroxyacetone phosphate (2) to glycerol 3-phosphate (1) by oxidizing one molecule of NADH to NAD⁺ as in the following reaction:

Reverse path

Glycerol-3-phosphate gets converted back to dihydroxyacetone phosphate by a membrane-bound mitochondrial glycerophosphate dehydrogenase, this time reducing one molecule of enzyme-bound flavin adenine dinucleotide (FAD) to FADH₂. FADH₂ then reduces coenzyme Q (ubiquinone to ubiquinol) which enters into oxidative phosphorylation.^[1] This reaction is irreversible.^[2

Function

The glycerol-3-phosphate shuttle allows the NADH synthesized in the cytosol by glycolysis to contribute to the oxidative phosphorylation pathway in themitochondria to generate ATP.^[1] It has been found in animals, fungi, and plants