The properties of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) from yeast and mammalian tissues have been studied extensively (2, 15). Bakers' yeast contains two native hexokinases, one of which (form P-II) may be activated by low concentrations of several metabolites (2, 10). Four isozymes of mammalian hexokinase have been identified and the proportions of these vary in different tissues (2,15,16). A feature of three of the forms of mammalian hexokinase is strong inhibition by glucose-6-P and this phenomenon is believed to be important in the regulation of hexokinase activity (2). The fourth enzyme form is a glucokinase (ATP:D-glucose 6-phosphotransferase, EC 2.7.1.2) which was first found in liver (7,18). A ketohexokinase (ATP:Dfructose I-phosphotransferase, EC 2.7.1.3), which phosphorylates fructose to give fructose-l-P, is also present in liver (3,8,14). This enzyme is sometimes referred to as a "fructokinase."Saltman (19) demonstrated hexokinase activity in extracts from several plant tissues and later workers have also reported the presence of the enzyme in plants (1, 4-6, 9, 13). Medina and Sols (12) noted the presence of a fructokinase (ATP:D-fructose 6-phosphotransferase, EC 2.7.1.4) in immature pea seeds. Fructokinase activity has been observed also in nectaries (6) and the conducting bundles of sugar beet leaf petioles (1 1).The situation in plants with respect to hexose kinases may be comparable in some ways to that in mammalian tissues. In an earlier publication it was shown that mature pea seeds contain several hexose kinases (20). Four fractions, designated I, II, III, and IV in order of elution from a DEAE-cellulose column, were obtained from (NH4)2SO4 fractions of pea seed extracts. Fraction I contained a glucokinase which had Km values of 0.07 mm and 30 mm for glucose and fructose, respectively (20). The fraction IV enzyme, fructokinase IV, was also characterized (21). This enzyme, a specific fructokinase with low activity toward glucose and mannose, had a requirement for K+ ions. Here, we describe the ' This investigation was supported by the University ofSydney Research Grant.properties of a different enzyme, fructokinase (fraction III), which was purified from fraction III. This enzyme will be referred to as fructokinase III. Fructokinase III was specific for fructose as substrate and had little activity with glucose. The enzyme was inhibited by fructose (in concentrations greater than 0.25 mM) and by ATP, Mg2+, MgATP, and MgADP. Glucose-6-P and fructose-6-P were only slightly inhibitory. Purification of Fructokinase III. Pea seeds were extracted and the hexose kinases fractionated on a DEAE-cellulose column as described previously (20). The fractions containing the first peak of fructose-phosphorylating activity (fraction III), but none of the fraction IV fructokinase, were pooled and concentrated to approximately 10 ml by ultrafiltration in a Diaflo apparatus (XM-50 membrane, 300 kPa/m2 nitrogen pressure). The concentrate was dialyzed against 10 mm Tris-HCl buffer (pH 8) and ...
A frutokinase (EC 2.7.1.4) was obtained from pea (Pisum sadvum L.) seeds. This enzyme, termed frctookinase (fraction IV), was specific for fructose as substrate and had little activity with glucose or mannose. Excess fructose inhbited the enzyme at the optimum pH (8.2) but not at pH 6.6. MgATP was inhibitory at pH 6.6. The apparent MichelisMenten constants at pH 8.2 were 0.057 mM for fructose and 0.10 mM for MgATP. Mg2+ ions were essential for activity; Mn2+ could partally replace Mg2+. Fructokinase (fraction IV) had a requirement for K+ ions which could be substantialy replaced by Rb+ or NH4+ but not by Na+. MATERIALS AND METHODSPea seeds obtained fro Glucose-6-P Phosphorylation of hexoses by ATP is usually the initial genase, P-gli reaction in the metabolism of these sugars. There are two NADH, ATI native isoenzymes of yeast hexokinase (ATP:i-hexose 6-phos-6-P-gluconat4 photransferase, EC 2.7.1.1) and these differ with respect to enolpyruvate glucose phosphorylation rates and regulatory properties (1, 11). galactose, L-S Mammalian hexokinases have been separated into four fractions tose, and D-n three of which are inhibited by glucose-6-P (1, 11). The other cal Co., or B fraction is a glucokinase (ATP:1-glucose 6-phosphotransferase, Preparatioi EC 2.7.1.2) originally found in liver (3,13,20). Liver glucoki-and defatted nase has a high km (12 mM) for glucose, a very high km (>800 powder and I mM) for fructose, and is not inhibited by glucose-6-P (1). Liver were carried also contains a ketohexokinase (ATP:u-fructose 1-phospho-dialyzed (NH transferase, EC 2.7.1.3) which phosphorylates fructose to yield fructose-phos fructose-i-P (2, 4, 7, 10). Ketohexokinase, sometimes referred DEAE-cellul to as "fructokinase," also acts on u-tagatose and, to a lesser with 0.025 extent, on L-sorbose (12).EDTA (buffi Plant hexokinases have been known for a considerable period in buffer A u but less definitive information is available. Saltman (14) ex-kinases were tracted hexokinase from several plant tissues and studied some 400 ml 0.27' properties of a preparation from wheat germ. This enzyme buffer A. Fr preparation phosphorylated glucose, fructose, mannose, and collected. Th glucosamine. Wheat germ hexokinases have been purified and the fraction I some physicochemical characteristics studied (5, 9). The pres-to approxima ence of a fructokinase (ATP:u-fructose 6-phosphotransferase, (PM-10 mem EC 2.7.1.4) in immature pea seeds was the subject of a brief arations of tl report by Medina and Sols (8 (Pisum sativum L. var. Progress No. 9) were m F. Cooper Ltd., Wellington, New Zealand. dehydrogenase, pyruvate kinase, lactate dehydrolucose isomerase, P-mannose isomerase, NADP, P and other nucleotides, glucose-6-P, fructose-6-P, e, 2-P-glycerate, 3-P-glycerate, 2,3-P2-glycerate, P-tris, MES, D-fructose, D-glucose, D-mannose, Dsorbose, 2-deoxy-D-glucose, D-glucosamine, D-taganannoheptulose were obtained from Sigma Chemiloehringer Mannheim GmbH. n of Fructokinase IV. Pea seeds were finely ground with ether (16). Extraction of th...
Understanding of asthma and co-management between patient and physician improves outcome. Feasibility of programs to achieve these goals in underserved settings is not documented. We used the Precede-Proceed model to document (a) community acceptance of a program to engage peer support of asthma management and care; (b) program revision to emphasize greater attention to availability of care and promotional events as channels for education; (c) engagement of intended audiences in planning and implementation; (d) participation of parents in program activities; and (e) peer-based education/support to reach parents, including socially isolated parents whose children experience heightened morbidity.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.