caa a22 4500 465745253 CHVBK 20180323111818.0 cr unu---uuuuu 170327e19900301xx s 000 0 eng 10.1007/BF02624724 doi (NATIONALLICENCE)springer-10.1007/BF02624724 A formula for quantifying the effects of substrate cycles (futile cycles) on metabolic regulation. Its application to glucose futile cycle in liver as studied by glucose-6-phosphatase/glucokinase determinations [Elektronische Daten] [Francesco Belfiore, Silvia Iannello] Summary: Substrate cycles (SC) are formed by a ‘forward pathway' (FP) and a ‘backward pathway' (BP), the difference between FP and BP forming the ‘metabolic flux' (MF) through the route of which the cycle is part. SC modulate regulatory effects, i.e. amplify or reduce the % change in MF compared to the % change in FP and BP, thus affecting the sensitivity to regulatory factors, including hormones. A formula is given to calculate (with an approximation of ± 0.5) the ‘flux response index' (FRI), i.e. the factor by which the % change in FP plus the % change in BP must be multiplied to obtain the % change in metabolic flux, when FP and BP undergo opposite, nonunidirectional changes (as is often the case in metabolic regulation). The formula is: FRI = [(FP+BP)/(FP-BP)]/2. By this formula we evaluated the hepatic activities of glucose-6-phosphatase and glucokinase (which roughly reflect hepatic glucose production and uptake, respectively), i.e. the two enzymes that catalyze the cycle between glucose-6-phosphate (glucose-6-P) and glucose. Based on data obtained in normal, nonobese diabetic and obese diabetic subjects as well as in normal, streptozotocin-diabetic, and obese diabetic (ob/ob) mice, we found that FRI was reduced in non-obese diabetic humans and animals whereas it was increased in obese-diabetic humans and mice, compared to normal controls. Thus, diabetes without obesitydecreases, and obesity with diabetesincreases, the sensitivity of the glucose-6-P/glucose cycle to regulatory agents. Casa Editrice «il Ponte», 1990 Futile cycles nationallicence Glucokinase nationallicence Glucose-6-phosphatase nationallicence Hormone sensitivity nationallicence Metabolic regulation nationallicence Substrate cycles nationallicence Belfiore Francesco Cattedra di Fisiopatologia del Ricambio, Istituto di Clinica Medica III, Università degli Studi di Cantania, Catania, Italy aut Iannello Silvia Cattedra di Fisiopatologia del Ricambio, Istituto di Clinica Medica III, Università degli Studi di Cantania, Catania, Italy aut Acta diabetologia latina Springer-Verlag 27/1(1990-03-01), 71-80 0001-5563 27:1<71 1990 27 592 https://doi.org/10.1007/BF02624724 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF02624724 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Belfiore Francesco Cattedra di Fisiopatologia del Ricambio, Istituto di Clinica Medica III, Università degli Studi di Cantania, Catania, Italy aut NATIONALLICENCE 700 1- Iannello Silvia Cattedra di Fisiopatologia del Ricambio, Istituto di Clinica Medica III, Università degli Studi di Cantania, Catania, Italy aut NATIONALLICENCE 773 0- Acta diabetologia latina Springer-Verlag 27/1(1990-03-01), 71-80 0001-5563 27:1<71 1990 27 592 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer