Terminal prostaglandin synthases have been identified that are responsible for the formation of other prostaglandins. For example, hematopoietic and lipocalin prostaglandin D synthases (hPGDS and lPGDS) are responsible for the formation of PGD 2 from PGH 2 . Similarly, prostacyclin (PGI 2 ) synthase (PGIS) converts PGH 2 into PGI 2 . A thromboxane synthase ( TxAS ) has also been identified. Prostaglandin-F synthase (PGFS) catalyzes the formation of 9α,11β-PGF 2α,β from PGD 2 and PGF 2α from PGH 2 in the presence of NADPH. This enzyme has recently been crystallized in complex with PGD 2  and bimatoprost  (a synthetic analogue of PGF 2α ).
5. A: Carbohydrate loading would be the most beneficial nutritional practice or technique for an individual preparing for a marathon. Carbohydrate loading is the intake of a large amount of carbohydrates for storage in the body, specifically, in skeletal muscle fibers. When athletes consume a high carbohydrate diet, they are able to store up to two times as many carbohydrates as normal. This additional energy will allow them to sustain physical activity for a longer period. As energy is needed, the body takes the stored carbohydrates and processes them through glucose catabolism, which has three stages: (1) glycolysis; (2) citric acid cycle; and (3) electron transfer system.