Table I.

Distribution of ATP sulfurylase and APS reductase in subcellular fractions from Arabidopsis leaf protoplasts isolated from 21- and 47-d-old plants

Fraction	Percent of Total Enzyme Activity
	Marker enzyme				Experimental enzyme
	PFP (cytosol)	NADP-GAPDH (chloroplast)	Cyt c oxidase (mitochondria)	HPR (peroxisome)	ATP sulfurylase	APS reductase
21-d-old plants
Chloroplasts	8 ± 2	93 ± 4	90 ± 5	72 ± 15	86 ± 7	96 ± 1
Mitochondria	<1	<1	10 ± 5	1 ± 1	2 ± 2	<1
Cytosol	92 ± 2	7 ± 4	<1	27 ± 16	12 ± 4	4 ± 1
Recovery	119 ± 30	94 ± 12	103 ± 30	105 ± 26	102 ± 26	81 ± 8
47-d-old plants
Chloroplasts	7 ± 3	95 ± 3	93 ± 3	82 ± 7	67 ± 3	95 ± 2
Mitochondria	1 ± 1	<1	7 ± 3	1 ± 1	<1	<1
Cytosol	93 ± 6	5 ± 3	<1	17 ± 6	33 ± 3	4 ± 3
Recovery	108 ± 30	104 ± 16	97 ± 20	104 ± 16	87 ± 23	85 ± 14

Each value is presented as a percentage of the total enzyme activity recovered in the three fractions, chloroplast, mitochondria, and cytosol. Also presented is the percentage of the enzyme recovered compared with an unfractionated protoplast lysate. Each value represents the mean ± sd of three independent fractionations. The enzyme activity value for each fractionation represents the mean of two measurements. The known localization of marker enzymes is indicated in parentheses. The marker enzymes are: HPR, hydroxypyruvate reductase; PFP, pyrophosphate: Fru-6-P 1-phosphotransferase; NADP-GAPDH, glyceraldehyde-3-phosphate dehydrogenase; Cyt c oxidase, cytochrome c oxidase.