Table 1.

Characterization of Substrate Specificity, Specific Activity, and pH Optima of Wild-Type and/or Mutant Forms of Hex

forms of Hex	MUG/MUGSa	nmol of MUG h−1 (μg of total protein)−1 b	αCRM/units of MUGc	μg of Hex/μg of total proteind	nmol of MUG h−1 (μg of Hex)−1 d	MUG pH optimum ± 0.2	MUGS pH optimum ± 0.2
pure Hex Se: 2(αNR424)	1.3 ± 0.3	1000 ± 100		1.0	1000 ± 100	4.1	4.0
WTf Hex S: 2(αNR424)	1.4 ± 0.2	69 ± 6	1.0	0.069	1000	4.0	3.9
Hex S: 2(αNK424)	1.9 ± 0.3	31 ± 2	0.68	0.021	1500	4.0	3.9
Hex S: 2(αDR424)	2.8 ± 0.7	15 ± 1	0.77	0.011	1400	4.2	4.1
Hex S: 2(αNQ424)	52 ± 15	78 ± 3	0.11	0.0086	9100	4.0	3.7
pure Hex Bg: 2(βDL454), pH 4.2/MUGS, pH 3	210 ± 30 55 ± 20h	10000 ± 1000d	N/Ai	1.0	10000 ± 1000	4.2	3.0
CHO negative controlj	0.7	0.04	0.0	0.0	0.0	N/A	N/A

^aThe ratio of units of MUG to MUGS hydrolyzed by the indicated form of Hex at pH 4.2 with substrate concentrations of 1.6 mM.

^bSpecific activity (SA) of the purified and partially purified forms of the Hex isozymes at pH 4.2 and 1.6 mM substrate.

^cRatio of the level on αCRM as determined by densitometry scanning of a Western blot (Figure 4) versus units of MUG activity, normalized against the expression of the wild-type αcDNA construct.

^dMicrograms of pure Hex per microgram of total protein calculated by (the SA of each Hex form) × (αCRM/units of MUG)/(the SA of pure Hex S).

^eData from ref 4.

^fWild type.

^gPurified placental Hex B.

^hDetermined at 4.2 for MUG and pH 3.0 for MUGS.

ⁱNot applicable.

^jThe untransfected CHO cell lysate was fractionated by DEAE ion-exchange chromatography in a manner identical to that of the transfected cell lysate.