Flying insects: model systems in exercise physiology

Insect flight is the most energy-demanding exercise known. It requires very effective coupling of adenosine triphosphate (ATP) hydrolysis and regeneration in the working flight muscles.³¹P nuclear magnetic resonance (NMR) spectroscopy of locust flight muscle in vivo has shown that flight causes only a small decrease in the content of ATP, whereas the free concentrations of inorganic phosphate (P _i ), adenosine diphosphate (ADP) and adenosine monophosphate (AMP) were estimated to increase by about 3-, 5- and 27-fold, respectively. These metabolites are potent activators of glycogen phosphorylase and phosphofructokinase (PFK). Activation of glycolysis by AMP and P _i is reinforced synergistically by fructose 2,6-bisphosphate (F2,6P₂), a very potent activator of PFK. During prolonged flight locusts gradually change from using carbohydrate to lipids as their main fuel. This requires a decrease in glycolytic flux which is brought about, at least in part, by a marked decrease in the content of F2,6P₂ in flight muscle (by 80% within 15 min of flight). The synthesis of F2,6P₂ in flight muscle can be stimulated by the nervous system via the biogenic amine octopamine. Octopamine and F2,6P₂ seem to be part of a mechanism to control the rate of carbohydrate oxidation in flight muscle and thus function in the metabolic integration of insect flight.Dedicated to Dr. Ernst Zebe, Emeritus Professor of Zoology (University of Münster) on the occasion of his 70th birthday.     

The Pasteur effect in facultative anaerobic metazoa

The existence and the regulatory mechanisms of the Pasteur effect in facultative anaerobic metazoa are discussed. There are three reasons for the controversy surrounding this phenomenon.1) The different definitions of the Pasteur effect,2) the antagonistic effect of metabolic depression and its species specific response to hypoxia, as well as3) the laboratory-specific differences in the experimental procedures for analyzing the Pasteur effect and its regulation. This review aims to clarify the confusion about the existence of the Pasteur effect in facultative anaerobic metazoa and to offer possible molecular mechanisms.     

Conservation,evolution, and specificity in cellular control by protein phosphorylation

The glycolytic control enzyme phosphofructokinase from the parasitic nematodeAscaris lumbricodies is regulated by reversible phosphorylation. The enzyme is phosphorylated by an atypical cyclic adenosine monophosphate (cAMP)-dependent protein kinase whose substrate specificity deviates from that of the mammalian protein kinase. This variation is explained by structural peculiarities on the surface part of the catalytic groove of the protein kinase. Also, the protein phosphatases responsible for the reversal of phosphorylation appear to act specifically in glycolysis and are different from those participating in regulation of glycogenolysis.     

Control of adenine nucleotide metabolism and glycolysis in vertebrate skeletal muscle during exercise

The turnover of adenosine triphosphate (ATP) in vertebrate skeletal muscle can increase more than a hundredfold during high-intensity exercise while the content of ATP in muscle may remain virtually unchanged. This requires that the rates of ATP hydrolysis and ATP synthesis are exactly balanced despite large fluctuations in reaction rates. ATP is regenerated initially at the expense of phosphocreatine (PCr) and then mainly through glycolysis from muscle glycogen. The increased ATP turnover in contracting muscle will cause an increase in the contents of adenosine diphosphate (ADP), adenosine monophosphate (AMP) and inorganic phosphate (P_i), metabolites that are substrates and activators of regulatory enzymes such as glycogen phosphorylase and phosphofructokinase. An intracellular metabolic feedback mechanism is thus activated by muscle contraction. How muscle metabolism is integrated in the intact body under physiological conditions is not fully understood. Common frogs are suitable experimental animals for the study of this problem because they can readily be induced to change from rest to high-intensity exercise, in the form of swimming. The changes in metabolites and effectors in gastrocnemius muscle were followed during exercise, post-exercise recovery and repeated exercise. The results suggest that glycolytic flux in muscle is modulated by signals from outside the muscle and that fructose 2,6-bisphosphate is a key signal in this process.     

大肠杆菌磷酸果糖激酶基因在野生型专性自养嗜酸性氧化硫硫杆菌Tt-Z2中的表达

利用PCR技术扩增E．coli K-12磷酸果糖激酶-1基因(pfkA)，将该基因与广泛寄主的IncQ质粒pJRD215连接构建重组质粒pSDK-1，该质粒可与pfk基因缺陷株E．coli DF1010互补．通过接合转移的方式将其导入专性自养极端嗜酸性氧化硫硫杆菌Tt-Z2中并得到表达．pSDK-1在宿主Tt-Z2中有较好的稳定性，在无选择压力条件下连续传50代仍可保留68％．酶活性测定表明，pSDK-1的pfkA基因在缺陷株E．coli DF1010中表达水平略高于出发菌株E．coli K-12；而在氧化硫硫杆菌中则以较低水平进行表达．葡萄糖可促进含pSDK-1的氧化硫硫杆菌Tt-Z2的生长，而对照菌株的生长则未受明显影响．说明重组菌可部分利用葡萄糖作为碳源而生长．