Table 1.

Characteristics of concentration domains at some molecular sinks.

Molecule		Diffusion coefficient (D; μm2 s−11)		Average concentration (u; mM)NB		Sink		Observed turnover number (q; s−11)		Amplitude		Maximum supply capacity (s−11)
ATP		500 (de Graaf et al., 2000)		5		Na+/K+ ATPase		48 (Lupfert et al., 2001)		0.9999		9.0 × 106
Glucose		500 (Vega et al., 2003)		1		GLUT1		187 (Barros et al., 2007)		0.9999		1.8 × 106
Pyruvate		120 (Pfeuffer et al., 2000)		0.1		LDH		269*		0.9941		4.5 × 104
Lactate		120 (Pfeuffer et al., 2000)		1.25		LDH		269*		0.9995		5.6 × 105
		120 (Pfeuffer et al., 2000)		1.25		MCT		85 (Ovens et al., 2010)		0.9998		5.6 × 105
Na+		1160 (Goodman et al., 2005)		10		Na+/K+ ATPase		144 (Lupfert et al., 2001)		0.9999		4.3 × 107
Ca2+		13 (Allbritton et al., 1992)		10−4		NCX		5000 (Shigekawa and Iwamoto, 2001)		<0		4.9
		13 (Allbritton et al., 1992)		10−4		PMCA		149*		<0		4.9
H+		37.8 (Vaughan-Jones et al., 2002)		4 × 10−5		NHE		2000 (Dixon et al., 1987)		<0		5.7
		37.8 (Vaughan-Jones et al., 2002)		4 × 10−5		MCT		85 (Ovens et al., 2010)		<0		5.7
		37.8 (Vaughan-Jones et al., 2002)		4 × 10−5		PMCA		298*		<0		5.7
		37.8 (Vaughan-Jones et al., 2002)		4 × 10−6		cytochrome oxidase		500*		<0		0.5

Domains were estimated assuming a sink radius a of 0.5 nm and a cell radius b of 10 μm, with the source located at the cell surface. NB, for simplicity concentration (u) is given in millimolar but note that unit consistency requires u to be entered in the equations as molecules/μm³ (and distances in micrometers). Na⁺/K⁺ ATPase (EC 3.6.3.9); GLUT1, glucose transporter isoform 1; LDH, lactate dehydrogenase (EC 1.1.1.27); MCT, proton-coupled monocarboxylate transporter; NCX, Na⁺/Ca²⁺ exchanger; PMCA, plasma membrane Ca²⁺ ATPase (EC 3.6.3.8); cytochrome oxidase (EC 1.9.3.1). Maximum supply capacities were estimated with Eq. 8, case II, by setting sink concentration equal to 0.

*BRENDA database, University of Cologne, Germany. The highest turnover numbers for mammalian enzymes are given.