摘要或動機

人類粒線體蘋果酸.可利用NAD⁺或NADP⁺為輔.，幫助腫瘤細胞獲得能量，但一般生理條件較傾向以NAD+為輔.。本研究將K346 修改成偏好NADP⁺之粒線體蘋果酸.家族中具有高度保留性的絲胺酸、及不具極性之丙胺酸，探討為何此酵素較偏好以NAD⁺為輔.。天然及突變株酵素的催化常數 (k_cat)、基質K_m 值、及抑制常數 (Kⁱ) 測定結果顯示K346 之點突變不會影響基質K_m 值，但K346S 之k_cat明顯上升，繼而改變此酵素對NADP+之選擇性。本研究對於人類粒線體蘋果酸.催化機制的了解，有助設計具專一性的活性抑制劑，未來可應用於抑制腫瘤細胞能量來源，進而抑制腫瘤細胞生長。;Human mitochondrial NAD(P)⁺-dependent malic enzyme can help tumor cells gain energy, using either NAD⁺ or NADP⁺ as the cofactor, but prefers NAD⁺ as the coenzyme. By mutating the K346 to Ser, conserved in NADP+-dependent ME and to Ala with non-polar, we explore why human mitochondrial NAD(P)⁺-dependent malic enzyme prefers NAD⁺ as the coenzyme. We measured the proteins k_cat, K_m and the K_i values. The experiments showed that mutantions don’t affect the K_m values, but K346S increased in the k_catvalue, transferring the coenzyme specificity to NADP⁺. If we develop deeper understanding of the human mitochondrial NAD(P)⁺-dependent malic enzyme, we can design a specific drag to inactivate the enzyme activity, and inhibit tumor cell growth.