Biochemical Properties of Lactate Dehydrogenase Eye-Specific C4 Isozyme: Lepomis macrochirus and Micropterus salmoides

The properties of lactate dehydrogenase (LDH, EC 1.1.1.27) eye-specific $C_4$ isozyme were studied by polyacrylamide gel electrophoresis, Western blotting, immunoprecipitation, and enzyme kinetics. Furthermore, we proposed the optimal conditions for measuring the activity of LDH eye-specific $C_4$ isozyme. The isozymes were detected in the cytosol of eye tissues from Lepomis macrochirus and Micropterus salmoides and were more similar to the $A_4$ than the $B_4$ isozyme. LDH/CS in the eye tissue of L. macrochirus was increased in September, so the ratio of anaerobic metabolism was high. The electrophoretic patterns of mitochondrial LDH were similar to those of cytosolic LDH in the eye tissues of L. macrochirus and Micropterus salmoides. LDH eye-specific $C_4$ isozyme from eye tissue was purified by preparative native-PAGE. The activities of LDH eye-specific $C_4$ isozymes in L. macrochirus and M. salmoides were reduced at concentrations greater than 0.2 mM and 0.1 mM of pyruvate, respectively. These concentrations remained at 5.2% and 15.8% as a result of the inhibition by 10 mM of pyruvate, so the degree of inhibition was very high. The LDH activities of eye tissues were reduced at concentrations greater than 22 mM and 24 mM of lactate, respectively, in L. macrochirus and M. salmoides. The ${K_m}^{PYR}$ of eye-specific $C_4$ was 0.088 mM in L. macrochirus and it was 0.033 mM in M. salmoides. The activities of cytosolic and mitochondrial eye-specific $C_4$ isozymes were high in ${\alpha}$-ketobutyric acid. Furthermore, the activities of eye tissue and eye-specific $C_4$ isozyme had to be measured with 0.5 mM of pyruvate and a buffer solution of pH 7.5. As a conclusion, the eye-specific $C_4$ isozyme in M. salmoides has a high affinity for pyruvate and exhibits maximum activity at a lower concentration of pyruvate and at higher concentration of lactate than that in L. macrochirus. Therefore, it seems that the energy produced by the LDH eye-specific $C_4$ isozyme in M. salmoides was used at the first stage of predatory behavior.

젖산탈수소효소 eye-specific C4 동위효소의 생화학적 특성: 파랑볼우럭(Lepomis macrochirus)과 큰입우럭(Micropterus salmoides)

눈조직의 젖산탈수소효소(LDH, EC 1.1.1.27) eye-specific $C_4$ 동위효소의 특성을 native-PAGE, Western blotting, 면역침강반응 및 효소 역학을 이용하여 연구하였고, LDH eye-specific $C_4$ 동위효소의 활성을 측정하는 조건을 제시하였다. 파랑볼우럭(Lepomis macrochirus)과 큰입우럭(Micropterus salmoides) 눈조직의 세포기질에서 LDH eye-specific $C_4$ 동위효소가 확인되었으며 $B_4$ 동위효소보다 $A_4$ 동위효소에 유사하였다. 파랑볼우럭 눈조직의 LDH/CS는 9월에 증가하여 혐기적 대사가 높게 이루어졌다. 파랑볼우럭과 큰입우럭 눈조직 미토콘드리아 LDH의 전기영동상은 세포기질 LDH와 유사하였다. 눈조직의 LDH eye-specific $C_4$ 동위효소는 Preparative native-PAGE에 의해 정제되었다. 파랑볼우럭과 큰입우럭의 LDH eye-specific $C_4$ 동위효소의 활성은 피루브산 0.2 mM과 0.1 mM 이상의 농도에서 각각 감소되었고, 피루브산 10 mM에서 5.2%, 15.8% 활성이 남아 저해 정도가 크게 나타났다. 그리고 눈조직의 LDH 활성도 젖산 22 mM과 24 mM 이상의 농도에서 각각 감소되어졌다. 파랑 볼우럭 eye-specific $C_4$ 동위효소의 $Km^{PYR}$는 0.088 mM, 큰입우럭 eye-specific $C_4$ $Km^{PYR}$는 0.033 mM였으며, 세포기질과 미토콘드리아 eye-specific $C_4$ 동위효소는 ${\alpha}$-ketobutyric acid에서 활성이 높게 나타났다. 눈조직과 eye-specific $C_4$ 동위효소의 활성은 피루브산 0.5 mM과 Tris-HCl 완충액, pH 7.5에서 측정하는 것이 적합한 것으로 확인되었다. 실험 결과, 큰입우럭 LDH eye-specific $C_4$ 동위효소는 파랑볼우럭 LDH eye-specific $C_4$보다 피루브산에 대한 친화력이 큰 것으로 확인되었고, 더 낮은 피루브산의 농도에서 최대 활성에 이르고, 더 높은 젖산의 농도에서 최대 활성을 나타냈다. 따라서 LDH eye-specific $C_4$ 동위효소에 의해 생성된 에너지가 포식 행동의 초기 반응에 사용되는 것으로 사료된다.