HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Katz, J. Articles by Bartsch, G. E. Search for Related Content PubMed PubMed Citation Articles by Katz, J. Articles by Bartsch, G. E. Social Bookmarking                      What's this?

The Pentose Cycle, Triose Phosphate Isomerization, and Lipogenesis in Rat Adipose Tissue

From the ¹ From the Institute for Medical Research, Cedars-Sinai Medical Center, Los Angeles 29, California, and the Departments of Medicine and Biochemistry and the Division of Biometry, Western Reserve University, Cleveland 6, Ohio

1. The relationship between the specific activities of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate from glucose-1-¹⁴C and -6-¹⁴C and triose-P isomerization has been analyzed. The specific activities are a function of three independent variables, the rate of triose-P isomerization, the contribution of the pentose cycle to glucose metabolism, and relative outflow from the dihydroxyacetone-P or glyceraldehyde-P pools. Equations to calculate the relative specific activities of these two compounds, the rate of triose-P isomerase, and the pentose cycle contribution under conditions of incomplete isotopic equilibration of triose-P have been derived. When synthesis of glycerol is limited, previously derived methods for evaluating the pentose cycle with the use of glucose-1-¹⁴C and -6-¹⁴C can be applied.

2. The contribution of the pentose cycle was calculated from ¹⁴C yields from glucose-1-¹⁴C and -6-¹⁴C, and from uniformly labeled ¹⁴C-glucose, and from degradation of glycerol derived from glucose-2-¹⁴C on incubation of epididymal fat tissue from rats. On the addition of epinephrine and growth hormone, similar estimates were obtained by three independent methods, theoretically valid in the absence of complete triose-P isomerization. Two methods, requiring complete equilibration, differed. Under other conditions, all five methods agreed closely.

The contribution of the pentose cycle was correlated with fatty acid synthesis. In tissue from rats fasted and refed, or with insulin stimulation, the contribution averaged 25%. In the presence of growth hormone it averaged 11%. In rats fed ad libitum and without hormone, the contribution averaged 14%, and 7% in the presence of epinephrine.

3. Specific activities of the triose phosphates from glucose-1-¹⁴C and -6-¹⁴C and their rates of isomerization were estimated for the intact adipose tissue. The relative rates ranged from 2 to 10 times those of glucose utilization and were not greatly affected by dietary conditions or hormones.

4. Glucose utilization by tissue from rats fasted and refed, with insulin present, was seven times as high as that of tissue from rats fed ad libitum and without insulin. Of the utilized glucose carbon, 38% appeared in CO₂, 45% in fatty acids, and 5% in glycerol. About two-thirds of the CO₂ was derived via pyruvate decarboxylation and one-third via the pentose cycle; very little CO₂ was evolved via the Krebs cycle. Epinephrine stimulated glucose utilization 3-fold. Of the glucose carbon, 30% appeared in CO₂, 7% in fatty acids, and 40% in glycerol. Over half of the CO₂ arose via the Krebs cycle, and one-tenth or less via the pentose cycle. Depending on diet and hormones, intermediate patterns between these two extremes were observed.

5. A balance of formation and utilization of reduced pyridine nucleotides in the cytoplasm was established. The total amount of reduced di- and triphosphopyridine-nucleotides formed in the cytoplasm was in small excess over hydrogen equivalents required for the synthesis of fatty acids, glycerol, and lactate. Under conditions of enhanced fatty acid synthesis, the TPNH formed via the pentose cycle was found to provide only 59 to 88% of the hydrogen required for fatty acid synthesis.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				Y. Si, J. Yoon, and K. Lee Flux profile and modularity analysis of time-dependent metabolic changes of de novo adipocyte formation Am J Physiol Endocrinol Metab, June 1, 2007; 292(6): E1637 - E1646. [Abstract] [Full Text] [PDF]

				K. L. McCormick, X. Wang, and G. J. Mick Evidence That the 11 {beta}-Hydroxysteroid Dehydrogenase (11 {beta}-HSD1) Is Regulated by Pentose Pathway Flux: STUDIES IN RAT ADIPOCYTES AND MICROSOMES J. Biol. Chem., January 6, 2006; 281(1): 341 - 347. [Abstract] [Full Text] [PDF]

				J. Schwender, J. B. Ohlrogge, and Y. Shachar-Hill A Flux Model of Glycolysis and the Oxidative Pentosephosphate Pathway in Developing Brassica napus Embryos J. Biol. Chem., August 8, 2003; 278(32): 29442 - 29453. [Abstract] [Full Text] [PDF]

				W.-N. P. Lee, L. G. Boros, J. Puigjaner, S. Bassilian, S. Lim, and M. Cascante Mass isotopomer study of the nonoxidative pathways of the pentose cycle with [1,2-13C2]glucose Am J Physiol Endocrinol Metab, May 1, 1998; 274(5): E843 - E851. [Abstract] [Full Text] [PDF]