Abstract: 【Aim】 The theoretical mole ratio of glucose (Glc) to pyruvate acid (PA), acetyl-CoA (AC), reduced nicotinamide adenine dinucleotide (NADH) and adenosine nucleoside triphosphate (ATP) is 1:2:2:10:30~32, while the theoretical activity ratio of hexokinase (HK) to phosphofructokinase 1 (PFK1), pyruvate kinase (PK), pyruvate dehydrogenase (PDH), citrate synthase (CS), mitochondria isocitrate dehydrogenase (ICDHm), α-ketoglutarate dehydrogenase (α-KGDH), NADH CoQ reductase (NCR), succinate CoQ reductase (SCR), CoQ cytochrome C reductase (CCR), cytochrome C oxidase (CCO) and ATP synthase (AS) is 1:1:2:2:2:2:2:10:2:12:12:26~28 in aerobic oxidation. This study aims to characterize aerobic oxidation in the silkgland of the silkworm,Bombyx mori, during the synthesis and secretion of silk proteins. 【Methods】 The contents of Glc, PA, AC, NADH and ATP, and the enzymatic activities of PFK1, PK, PDH, CS, ICDHm, α-KGDH, NCR, SCR, CCR, CCO and AS were determined using spectrophotometric and high performance liquid chromatographic methods. 【Results】 In the silkgland of B. mori, Glc was undetectable, and the molar concentration increased in the order of 1/30 ATP, 1/10 NADH, 1/2 AC and 1/2 PA during the synthesis and secretion of silk proteins. Among the related enzymes of glycolysis, the PFK1 activity was the lowest; the activities of the related enzymes of tricarboxylic acid cycle increased in the order of 1/2 ICDHm, 1/2 α-KGDH and 1/2 CS; the activities of the related enzymes of oxidative phosphorylation increased in the order of 1/26 AS, 1/10 NCR, 1/2 SCR, 1/12 CCR and 1/12 CCO, with the 1/26 AS activity the lowest. During the synthesis and secretion of silk proteins, the activities of 1/26 AS, 1/2 ICDHm, 1/2 PDH and PFK1 increased sequentially. The concentrations of NADH and ATP and the activities of PFK1, PDH and NCR generally increased during the synthesis of silk proteins but decreased during the secretion of silk proteins. 【Conclusion】 It is so inferred that PFK1, ICDHm and AS are the ratelimiting enzymes of glycolysis, tricarboxylic acid cycle and oxidative phosphorylation, respectively, the rates of glycolysis, pyruvate dehydrogenation, tricarboxylic acid cycle and oxidative phosphorylation decrease progressively in the silkgland during the synthesis and secretion of silk proteins, and the rates of aerobic oxidation increase during the synthesis but decrease during the secretion of silk proteins.

Key words: Bombyx mori, silkgland, silk protein, aerobic oxidation, rate-limiting enzyme