Table 4. Estimated rates of total NAD synthesis (“amidated” plus “deamidated”) in mouse tissues.

	In vivo total NAD synthesis ratea	amidated route	deamidated route	NAD turnover half-lifeb
	nmol/min/g	relative	relative %	min
skeletal muscle	∼1.1	≧99.9	≤0.1	∼300
lung	∼0.6	≧99.9	≤0.1	∼250
kidney	∼15	99.9	0.1	∼30
brain	∼0.9	99.9	0.1	∼240
spleen	∼1.2	98.4	1.6	∼130
small intestine	∼1.7	97.2	2.8	∼90
heart	∼5.2	99.3	0.7	∼85
liver	∼21	99.1	0.9	∼30
blood	∼0.01	90.9	9.1	∼2850

^aSum of estimated rates of “amidated” (Table 2) and deamidated routes (Table 3).

^bValues are calculated by the equation (4) shown in Methods, using the in vivo total NAD synthesis rate as “v” value (assumed to equal the in vivo total NAD degradation rate), and the NAD level in each tissue (Figure 4).