Table 1.

Cell Uptake of Secreted Lysosomal Enzymes Phosphorylated by Endogenous GlcNAc-1-Phosphotransferase or Overexpressed WT Enzyme or the S1-S3 Mutant

Enzyme	PTase	Total Units Added	Man-6-P	% Uptakea		Fold Increase
					M6PR Dependent
LAMAN	endogenous	670	−	0.76 ± 0.23	0.14
			+	0.62 ± 0.27
	WTα/β	359	−	24.70 ± 1.34	21.5	153
			+	3.20 ± 0.77
	S1-S3	530	−	22.46 ± 4.07	18.2	130
			+	4.30 ± 1.19
GAA	endogenous	5.7	−	4.05 ± 0.46	3.8
			+	0.22 ± 0.42
	WTα/β	3.8	−	3.31 ± 1.13	2.9	0.8
			+	0.44 ± 1.16
	S1-S3	3.2	−	12.79 ± 0.90	9.8	2.6
			+	2.99 ± 1.59
GBA	endogenous	2.7	−	10.74 ± 1.94	5.1
			+	5.65 ± 1.51
	WTα/β	2.3	−	46.73 ± 4.00	37.4	7.3
			+	9.37 ± 1.26
	S1-S3	2.8	−	49.74 ± 11.53	41.1	8.0
			+	8.67 ± 4.21
GLA	endogenous	194	−	2.72 ± 0.91	1.7
			+	1.00 ± 0.11
	WTα/β	141	−	9.53 ± 0.11	8.2	4.8
			+	1.30 ± 0.13
	S1-S3	237	−	7.01 ± 0.69	6.1	3.5
			+	0.95 ± 0.11

One unit = 1 nmol 4-methylumbelliferone released per hour. Uptake experiments were performed in either the absence or the presence of 5 mM Man-6-P.

^aPercentage uptake per 200 μg cell protein in 24 hr.