Even though one might argue that this lends a false sense of quantitative objectivity to an evaluation of an article or series of articles, these conversions are fairly basic. Researchers sometimes do these conversions to get a crude sense of the intracellular concentrations, based on data expressed in nmol of substance per g tissue or per 10^6 cells, etc.
Intracellular Water Per Gram of Wet Weight of Tissue:
Yamada et al. (2000) [Kazuhiro Yamada et al., 2000: (http://jn.nutrition.org/cgi/content/full/130/8/1894) (http://www.ncbi.nlm.nih.gov/pubmed/10917899?dopt=Abstract)] includes a cited value for the cytosolic volume (~intracellular water) as 0.4 mL/g fresh weight (wet weight) of the liver.
Kimoto et al. (2001) [Tetsuya Kimoto et al., 2001: (http://endo.endojournals.org/cgi/content/full/142/8/3578) (http://www.ncbi.nlm.nih.gov/pubmed/11459806?dopt=Abstract)] estimated that hippocampal tissue contained 0.7-0.8 mL intracellular water/g ww.
Fatouros and Marmarou (1999) [Fatouros and Marmarou, 1999: (http://www.jnsonline.org/jns/issues/v90n1/pdf/n0900109.pdf) (http://www.ncbi.nlm.nih.gov/pubmed/10413163)] found that the average water content of white matter and gray matter were 0.68 mL/g ww and 0.8 mL/g ww. These measurements encompass both the intracellular and extracellular fluid water contents, however. Fatrouros et al. (1999) excluded the volume of water in the cisterns, etc., and argued that "most" of the water in the gray matter is intracellular but that about 15 percent of the water in the white matter is extracellular. Some of the values for the gray matter, listed in table 3, are, however, between 0.75 and 0.8 mL/g ww.
Aliev et al. (2002) [Aliev et al., 2002: (http://www.ncbi.nlm.nih.gov/pubmed/11744012)] estimated the intracellular water content of the rat heart to be 0.615 mL/g wet mass. They also estimated that the extracellular water content is about .174 mL/g wet mass (which is part interstitial fluid and part water in blood vessels, in blood).
Cellular Protein Per Gram of Wet Weight of Tissue:
Bissell et al. (1973) [D. Montgomery Bissell et al., 1973: (http://jcb.rupress.org/cgi/content/abstract/59/3/722) (http://www.ncbi.nlm.nih.gov/pubmed/4357460?dopt=Abstract)] cites a value of 22 percent cellular protein for whole liver (0.22 g protein/g ww liver).
Maia et al. (2005) [Ana Luiza Maia et al., 2005: (http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1190373)] give values of 150 g cellular protein/1500 g wet weight (0.1 g protein/g ww) of liver and 2,240 g cellular protein/28,000 g wet weight of muscle (0.08 g protein/g ww).
Kimoto et al. (2001) [Tetsuya Kimoto et al., 2001: (http://endo.endojournals.org/cgi/content/full/142/8/3578) (http://www.ncbi.nlm.nih.gov/pubmed/11459806?dopt=Abstract)] found that hippocampal tissue contained 0.96 (+/- 0.02) mg protein/10 mg wet weight (0.094-0.098 mg protein/mg ww).
Ratio of Wet Weight to Dry Weight of Tissue:
This article (Wimmer et al., 1985) [Wimmer et al., 1985: (http://www.ncbi.nlm.nih.gov/pubmed/4086343)] found that the livers of male rats contained 3.33 (+/- 0.3) g wet weight/g dry weight of liver. They found that the livers of female rats contained 3.28 (+/- 0.24) g wet weight/g dry weight liver. The authors recommended that the converstion factor of 3.3 g ww/g dw be used in general.
This article (Ronglih Liao et al.) has some good references on these conversions:
http://circres.ahajournals.org/cgi/content/full/78/5/893#R34
(pubmed: http://www.ncbi.nlm.nih.gov/pubmed/8620610?dopt=Abstract)
0.125 (+/- 0.004) mg Lowry protein/mg wet weight heart for control white turkeys (turkey "poults")
0.087 (+/- 0.003) mg Lowry protein/mg ww for hearts of turkeys with cardiomyopathy
Cited assumption for intracellular (cytosolic) water volume in myocytes of control animals and animals with dilated cardiomyopathy: 0.5 mL intracellular water/g wet weight of heart tissue.
In the turkey heart: 0.218 = (g dry weight/g wet weight), for both failing and healthy hearts, or 4.59 g ww/g dry weight.
[Note: the Lowry protein content is an estimate of the intracellular protein content (the intracellular proteins have a higher content of aromatic amino acid residues) and excludes the influence of extracellular proteins on the measurement]
Here's another one (Jie Shang et al.) that uses a 0.5 g protein/mL intracellular water for "packed fibroblasts" in culture:
http://www.ncbi.nlm.nih.gov/pubmed/14729664?dopt=Abstract
This article (David Cichowicz et al.) used a conversion of 18.1 nmol/g ww for the liver of intracellular total folates and calculated an intracellular total folates concentration of 25 uM. I won't extrapolate their conversion factor now, but there it is:
http://www.ncbi.nlm.nih.gov/pubmed/3828321
This article (William Strong and coauthor) uses the assumption that there's 0.7 mL intracellular water/g wet weight of rabbit liver:
http://www.ncbi.nlm.nih.gov/pubmed/2514800
Lund and Wiggins (1987) [Lund and Wiggins, 1987: (http://www.ncbi.nlm.nih.gov/pubmed/3620602)] cites and calculates multiple values for the cytosolic water volume per g ww of liver, and some of the numbers are 0.489 mL/g ww, 0.526 mL/g ww, and 0.55 mL/g ww. The 0.4 mL/g ww is seeming, more and more, to be an unusually low value. I'm going to increase the standard conversion factor I use to reflect the use of 0.7 mL/g ww tissue in different cell types. The Cichowicz conversion used 0.72 mL/g ww, Strong et al. used 0.7, Liao cited a value of 0.5, Kimoto used 0.7-0.8 (let's say that's 0.75), and then 0.489 from Table 1 in Lund and Wiggins (1.86/3.8), 0.55 (cited on p.63 of Lund and Wiggins), and 0.4. The average is 0.514, but I'm going to use 0.615 as a value, from Aliev et al. (2002) (see "Summary" below).
That above article (Lund and Wiggins, 1987) also includes these values for 1 mL intracellular water per cell numbers of liver parenchymal cells:
(4.15 x 10^8 cells/g dw) x (1 g dw/3.58 g ww) x (1 g ww/0.6 mL intracellular water) = 1.932 x 10^8 cells/mL intracellular water = 1.159 x 10^8 cells/g ww
They also cite a value of 4.34 x 10^8 cells/g dw, which would convert to:
(4.34E8) x (1/2.148) = 2.02 x 10^8 cells/mL intracellular water = 1.212 x 10^8 cells/g ww
This article uses a value of 1.9 x 10^8 human fibroblasts/mL intracellular water, which converts to 1.14 x 10^8 cells/g ww (using the 0.6 mL intracellular water/g ww value) [Foo et al., 1982: (http://jn.nutrition.org/cgi/content/abstract/112/8/1600) (http://www.ncbi.nlm.nih.gov/pubmed/7047695?dopt=Abstract)].
McDevitt et al. (2005) [Theresa McDevitt et al., 2005: (http://www.ncbi.nlm.nih.gov/pubmed/15671207)] used values of 0.909-1.25 mg cellular protein/10^6 cells (monocyte-macrophage-lineage, U937 cells):
(0.909 mg protein/10^6 cells) x (1 g ww/100 mg protein) x (0.6 mL intracellular water/1 g ww) = 0.00545 mL/10^6 cells = 1.83 x 10^8 cells/mL intracellular water
or, for the 1.25 value, the conversion gives 1.33 x 10^8 cells/mL intracellular water
I'll use 1.9 x 10^8 cells/mL intracellular water as a conversion factor (looking at the different results)
Culic et al. (1999) [Ognjen Culic et al., 1999: (http://ajpcell.physiology.org/cgi/content/full/276/5/C1061) (http://www.ncbi.nlm.nih.gov/pubmed/10329953)] used these conversion factors for porcine aortic endothelial cells and for the heart tissue overall:
1 mg cellular protein/5.4 x 10^6 cells (in porcine aortic endothelial cells) (gives 0.185 mg protein/10^6 cells)
10 ug triglycerides/1.1 x 10^(-8) mol triglycerides (average molecular weight of triglycerides assumed to be 900 g/mol)
17 ug triglycerides/mg protein in endothelial cells
140 mg protein/1 g of myocardial tissue
Summary:
To convert nmol/g wet weight to intracellular concentration in nM:
(Y nmol/g ww) x (1 g ww tissue/0.615 mL intracellular water) x (1000 mL intracellular water/1 L cytosolic water) = (Y) x (1626) = Z nM (across whole tissue).
To convert nmol substance Y/g cellular protein into nM, use the assumption that 10 percent of the wet weight of the tissue is protein (100 mg protein/g ww):
(Y nmol/g protein) x (0.10 g protein/g ww) x (1 g ww/0.615 mL intracellular water) x (1000 mL intracellular water/1 L intracellular water) = (Y) x (163) = Z nM (intracellular).
Basic conversion factors for folic acid and reduced folates:
1 nM serum folate = 2.265 ng/mL
Molar mass of folic acid: 441.4 g/mol
Molar mass of 5-formyltetrahydrofolate (5-CHO-THF): 473.44 g/mol
Molar mass of 10-formyltetrahydrofolate (10-CHO-THF): 473.44 g/mol
Molar mass of 5-methyltetrahydrofolate (MTHF): 459.46 g/mol
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