Biosynthesis of Squalene and Cholesterol in the Fish : I. In Vitro Studies on Acetate Incorporation

アセテート-1-14Cからのスクワレンおよびコレステロールの生合成に関し,コイの肝膵臓,ニジマス肝臓およびマウス肝臓のホモジネート上澄液を用いて研究した.補酵素ATP,NAD,NADPおよびNADPHを添加し,30℃で好気的・嫌気的条件下に培養を行なった.

アセテートの総脂質中へのとり込みは,ニジマス標品を用いた場合は非常に活潑で,コイ標品でもかなりな程度行なわれたが,マウス標品では著しく低い結果を得た.コイおよびニジマスで代表される魚類標品での脂肪酸合成はステロール合成を凌駕していたが,マウス標品では逆にコレステロール合成が優れていた.

一般的に魚類におけるコレステロール合成に関する補酵素要求性は陸上動物のそれとあまり相違してはいない.

スクワレンからコレステロールへの閉環に関し要求される補助因子の一つとして,好気的条件下の合成にみられたように,分子状酸素が重要に作用する.さらに,深海産のサメ肝油中にみられる異常な程の大量なスクワレンとそれ程でもないコレステロールの含量に関して考察を加えた.

The biosynthesis of squalene and cholesterol from acetate-1-14C has been studied in the homogenate supernatant of carp hepatopancreas, rainbow trout liver and mouse liver. The incubation was carried out with the addition of ATP, NAD, NADP and NADPH at 30℃ for certain periods of time under aerobic and anaerobic conditions.

It was shown that the incorporation of acetate-l-14C into the total lipids was very active in the preparation of rainbow trout liver, less active in carp hepatopancreas, and low in mouse liver. In the fish preparation represented by carp and rainbow trout, the de novo synthesis of the fatty acids exceeds of the sterols. On the contrary, the cholesterogenesis surpasses the lipogenesis in the mouse liver preparation.

In general, the coenzyme requirements for the cholesterol synthesis in the fish are not markedly different from those needed by land animals.

As one of the cofactors required for the cyclization of squalene to lanosterol, the molecular oxygen is very important as shown in the case of aerobic condition. Moreover, it was discussed why certain deep sea sharks contain extraordinarily high amounts of squalene and little cholesterol in their liver oils.