Comp. Biochem. Physiol. Vol. 101B,No. !/2, pp. 135-138, 1992 0305-0491/92$5.00 + 0.00 Printedin Great Britain © 1992Pergamon Presspie ALLOSTERIC CONTROL OF 6-PHOSPHOFRUCTO-1-KINASE FROM RAT LUNG ABUELGASSlM O. ABUELGASSIM, AHMED M. SALEM and SAMIR M. KaOJA* Department of Biochemistry,Faculty of Science,King Abdulaziz University, P.O. Box 9028, Jeddah-21413, Saudi Arabia (Tel:02 695-2289);(Fax: 02 640-0736) (Received 19 June 1991) Abstract--1. The regulation of 6-phosphofructo-1-kinase(PFK) in the rat lung of normally fed (control), 72 hr-starved and streptozotocin-induced diabetic rats was investigated. 2. No significant changes in the total enzymeactivitiesand the activity ratios [activityat 0.5 mM fructose 6-phosphate at pH 7.0/activity at pH 8.0 (vo.5/V)] of rat lung were observed between the control and 72 hr-starved or streptozotocin-induced diabetic rats. 3. Rat lung PFK was highly stimulated by fructose 2,6-bisphosphate (Fru-2,6-P:) as the affinity of the enzyme for fructose 6-phosphate was highly increased by this metabolite and the enzyme inhibition by ATP was released. 4. Although rat liver and mucosal PFK were found to be highly sensitiveto stimulation by Fru-2,6-P 2, lung PFK was significantly more sensitive to the stimulation by this metabolite than the other tissues. 5. The enzyme was highly inhibited by citrate and was only slightly inhibited by phosphocreatine. 6. ADP, AMP and c-AMP were shown to be activators of lung PFK with c-AMP being the most effective activator. 7. As a rate limiting enzyme of glycolysis, rat lung PFK is highly controlled by its allosteric effectors, especially Fru-2,6-P2,possibly for surfactant lipid synthesiswhich usually requires a high rate of glycolysis. INTRODUCTION The lung is an organ that has one of the highest PO: in the body. It has been reported that considerable quantities of lactate are produced by the lung (Rhoades et al., 1978; Wolfe et al., 1979). About 30--60% of the glucose consumed in the lung is converted to lactate (Yeager and Massaro, 1972; Ayuso et aL, 1973; Tierney and Levy, 1976). The production of lactate increased when lung was subjected to hypoxic conditions (Bassett et al., 1974; Rhoades et aL, 1975; Kerr et al., 1979) or perfused with 2,4-dinitrophenol (Bassett and Fisher, 1976). It is well known that 6-phosphofructo-l-kinase (PFK : EC 2.7.1.11) is a key regulatory enzyme con- trolling the glycolytic pathway and its activity is affected by alterations in hormonal, nutritional, pathological and devlopmental states (Gualberto et al., 1987; Heesbeen et al., 1987; Khoja et al., 1988; Khoja and Abuelgassim, 1991). However, during perinatal development of rat lung, the activity and isoenzyme patterns of PFK were studied (Rijksen et al., 1985; Heesbeen et al., 1987) as the enzyme activity increased until day 20 of gestation followed by a rapid fall until 2 days post-partum, whereas no change in subunit composition during this period was observed. Moreover, Heesbeen et al. (1989) reported that PFK from foetal and adult rat lung consisted of L, M and C subunits in a ratio of 65 : 25 : 10. Fructose 2,6-bisphosphate (Fru-2,6-P2) has been described as the most potent stimulator of PFK (Van Sehaftingen et al., 1980). This metabolite plays an *Author to whom correspondence should be addressed. important role in the control of glycolysis in mam- malian tissues (for a review see Hue and Rider, 1987). In this paper, the allosteric control of lung PFK was studied in starved, streptozotocin-induced dia- betic and normally fed rats to provide information on PFK regulation. MATERIALS AND METHODS Materials Biocbemicals were purchased from Sigma Chemical Co. (Poole, England) and used without further purification. All other chemicalwere purchased from BDH (Poole, England). Sephadex G-100 was purchased from Pharmacia Fine Chemicals (Uppsala, Sweden). Animals Adult male Wistar rats (190-230 g) were obtained from King Fahd Medical Research Centre, King Abdulaziz Uni- versity, Jeddah, Saudi Arabia. Rats were either fed ab lititum on a standard laboratory diet (Grain Soils and Flour Mills Organization, Jeddah, Saudi Arabia) or starved for 72 hr with free access to water. Diabetes was induced by a single intravenous injection of streptozotocin (65 mg/kg of body wt in 50 mM sodium citrate, pH 4.5). Rats showing positive glycosuria (>400mg/100ml, Dextrostix reagents strips, Ames Division, Miles Lab., England) 4 days after induction of diabetes were used. Assay of Fru-2,6-P~ Fru-2,6-P 2 was measured in rat lung using the method described by Van Schaftingen et al. (1982) with stimulation to PPi-dependent phosphofructokinase (EC 2.7.1.90) purified from potato tubers. Preparation of extracts and gel filtration Animals were anaesthetized with Sagatal (0.1 mi]100g body wt) and the lungs were quickly removed and frozen 135