Meeting Abstract
P2.126 Monday, Jan. 5 Arrest of aerobic metabolism in Artemia franciscana embryos during diapause PATIL, Y.N.*; MENZE, M.A.; HAND, S.C.; Louisiana State University, Baton Rouge; Louisiana State University, Baton Rouge; Louisiana State University, Baton Rouge ypatil1@lsu.edu
Diapause embryos of the brine shrimp, Artemia franciscana, are characterized by a low metabolic rate. Based on our previous data, we hypothesized that metabolic arrest is due to a combination of at least two mechanisms, namely substrate limitation to the mitochondrion and reversible inhibition of oxidative phosphorylation. We measured metabolic intermediates in metabolically-active embryos and in diapause embryos. A significant reduction in glucose-6-phosphate was evident in diapause (0.22 +/- 0.02 nmol/mg embryo protein; mean SE, n = 3) versus active (1.85+/- 0.53 nmol/mg) embryos. Values for glucose in diapause (5.98 +/- 1.8 nmol/mg) and active (3.58 +/- 2.09 nmol/mg) embryos allow the calculation of mass action ratios (0.04 diapause vs. 0.52 active), which indicate inhibition at the hexokinase (HK) step and suggest a reduced glycolytic flux and substrate limitation to the mitochondrion in diapause. Pyruvate is lower in diapause (0.24 +/- 0.04 nmol/mg) than in active (0.46 +/- 0.08 nmol/mg) embryos, but not as low as anticipated, despite being downstream of the glycolytic inhibition at HK. This observation could be explained by an inhibition of pyruvate dehydrogenase (PDH). Measurement of acetyl CoA levels and kinetic characterization of PDH are underway to evaluate this possibility. To further infer sites of respiratory inhibition, we measured the apparent Km of Complex IV (cytochrome c oxidase) for cytochrome c (cyt c). The value in diapause embryos (30.3 +/- 3.5 M; mean SE, n = 3) was significantly higher than in active embryos (12.6 +/- 3.9 M). Whether or not this reduction in apparent affinity has any impact on flux through Complex IV depends on estimates of cyt c level in the intermembrane space. [Supported by NIH grant 2 RO1 DK04670-14A1]
