Table 2.

Total amount of CO production and heme turnover in olfactory receptor neuron

Heme precursors and metabolites	Labeling with [¹⁴C]glycine			Labeling with [³H]ALA
	¹⁴C-labeled products	Total amount	Newly synthesized amount from glycine^2_a	³H-labeled products	Total amount
	(pmol/mg protein per 6 hr)			(pmol/mg protein per 6 hr)
Glycine	1,200
ALA	100		3400	36
Heme	5.3	1500^b	180	1.2	1,500^b
CO	2.9	1600^2_c	95
Bilirubin				0.23	570^2_c

Primary cultures of olfactory receptor neurons were incubated with [¹⁴C]glycine or [³H]ALA for 6 hr. Then cellular uptakes of these precursors and biosynthesis of [¹⁴C]ALA, [¹⁴C]heme, ¹⁴CO, [³H]heme, and [³H]bilirubin were measured in these cell cultures.
↵F2_a Taking into account the endogenous free glycine level in neuron cells (20 nmol/mg protein), total amounts of newly synthesized products from glycine were calculated as described below. Average concentration of cellular [¹⁴C]glycine was 600 pmol/mg protein. Newly synthesized amount from glycine = ¹⁴C-labeled amount × (total glycine)/(average [¹⁴C]glycine) ^bThe cellular heme concentration was determined spectrophotometrically and expressed as pmol/mg protein.
↵F2_c The total amount of production was calculated as described below. Total amount of production=¹⁴C (or³H)-labeled production×(total heme)/[average [¹⁴C]heme (or [³H]heme)]