Abstract
Isolated rat hepatocytes were incubated with [3-14C]xylitol or d-[3-14C]xylulose plus xylitol or glucose at substrate concentrations. The glucose formed was isolated and degraded to give the relative specific radioactivities in each carbon atom. C-4 of glucose had the highest specific radioactivity, followed by C-3, with half to one-fifth that of C-4. Only about 1% of the total radioactivity was in C-1. The data are compared with the predictions of the classical pentose phosphate cycle [Horecker, Gibbs, Klenow & Smyrniotis (1954) J. Biol. Chem. 207, 393–403], and the proposed new version of the pentose phosphate cycle in liver [Longenecker & Williams (1980) Biochem. J. 188, 847–857], which they denoted as the `L-type pentose cycle'. The Williams pathway predicts that the specific radioactivity of C-1 of glucose should be half that of C-4 (after correction for approximately equal labelling on C-3 and C-4 of hexose phosphate in the pathway involving fructose 1,6-bisphosphatase). The actual labelling in C-1 is 20–350-fold less than this. When the hepatocytes are incubated with phenazine methosulphate, to stimulate the oxidative branch of the pentose phosphate cycle, the predicted relationship between (C-2/C-3) and (C-1/C-3) ratios of specific radio-activities is nearly exactly in accord with the classical pentose phosphate cycle. Glucose and glucose 6-phosphate were isolated and degraded from an incubation of hepatocytes from starved/re-fed rats with [3-14C]xylitol. Although the patterns were of the classical type, there was more randomization of 14C into C-2 and C-1 in the glucose 6-phosphate isolated at the end of the incubation than in the glucose which was continuously produced.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- HORECKER B. L., GIBBS M., KLENOW H., SMYRNIOTIS P. Z. The mechanism of pentose phosphate conversion to hexose monophosphate. I. With a liver enzyme preparation. J Biol Chem. 1954 Mar;207(1):393–403. [PubMed] [Google Scholar]
- Katz J., Wals P. A., Rognstad R. Glucose phosphorylation, glucose-6-phosphatase, and recycling in rat hepatocytes. J Biol Chem. 1978 Jul 10;253(13):4530–4536. [PubMed] [Google Scholar]
- Longenecker J. P., Williams J. F. Quantitative measurement of the L-type pentose phosphate cycle with [2-14C]glucose and [5-14C]glucose in isolated hepatocytes. Biochem J. 1980 Jun 15;188(3):859–865. doi: 10.1042/bj1880859. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Longenecker J. P., Williams J. F. Use of [2-14C]glucose and [5-14C]glucose for evaluating the mechanism and quantitative significance of the 'liver-cell' pentose cycle. Biochem J. 1980 Jun 15;188(3):847–857. doi: 10.1042/bj1880847. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Rognstad R., Katz J. The mechanism of the non-oxidative segment of the pentose cycle in the liver. Biochem Biophys Res Commun. 1974 Nov 27;61(2):774–780. doi: 10.1016/0006-291x(74)91024-9. [DOI] [PubMed] [Google Scholar]
- Rognstad R. [14C] distribution in glucose formed from pyruvate in rat hepatocytes. Int J Biochem. 1980;12(3):509–510. doi: 10.1016/0020-711x(80)90139-1. [DOI] [PubMed] [Google Scholar]
- Schmidt K., Genovese J., Katz J. Enzymic degradation of isotopically labeded compounds. II. Glucose labeled with 14C and tritium. Anal Biochem. 1970 Mar;34:170–179. doi: 10.1016/0003-2697(70)90098-9. [DOI] [PubMed] [Google Scholar]
- Williams H. R., Landau B. R. Pathways of fructose conversion to glucose and glycogen in liver. Arch Biochem Biophys. 1972 Jun;150(2):708–713. doi: 10.1016/0003-9861(72)90089-6. [DOI] [PubMed] [Google Scholar]
- Williams J. F., Blackmore P. F., Clark M. G. New reaction sequences for the non-oxidative pentose phosphate pathway. Biochem J. 1978 Oct 15;176(1):257–282. doi: 10.1042/bj1760257. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Williams J. F., Clark M. G., Blackmore P. F. The fate of 14C in glucose 6-phosphate synthesized from [1-14C]Ribose 5-phosphate by enzymes of rat liver. Biochem J. 1978 Oct 15;176(1):241–256. doi: 10.1042/bj1760241. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wood T., Gascon A. A lack of reactivity of D-arabinose 5-phosphate with enzymes of the pentose phosphate pathway. Arch Biochem Biophys. 1980 Sep;203(2):727–733. doi: 10.1016/0003-9861(80)90232-5. [DOI] [PubMed] [Google Scholar]