Table 1. .

Determination of MHBD Activity^[Note]

	Amount (%) of Activity
Protein	Patient IV-1	Patient IV-3	Control 1	Control 2
2-Methyl-acetoacetyl-CoA	2.28 (90)	2.02 (80)	2.62 (104)	2.42 (96)
Acetoacetyl-CoA	89 (130)	76 (111)	74 (108)	63 (92)
Ratio	.026 (70)	.027 (73)	.035 (95)	.039 (105)

Note.— The amount is indicated in nmol/min/mg (percentage of control average). The activity in cultured Epstein Barr–virus immortalized lymphoblastoid cell lines from two patients with MRXS10 and from two unaffected control subjects was measured spectrophotometrically in the reverse direction by following the decrease in absorbance at 340 nm at 37°C. Acetoacetyl-CoA was measured as a reference. The standard reaction medium, with a total volume of 250 μl, contained the following components: 50 mM MES/100 mM potassium phosphate buffer (pH 6.16), 0.1% (wt/vol) Triton X-100, 0.2 mM NADH, and 0.32 mg/ml lymphoblastoid cell homogenate protein. Reactions were started by the addition of 2-methyl-acetoacetyl-CoA at a final concentration of .05 mM. Activity is given as a mean of two independent measurements.