A new quantitative analytical method of serum biotinidase activity using biocytin as a substrate and its clinical significance in Japan.

We have developed a new quantitative analytical method of serum biotinidase activity, which uses the native substrate biocytin, and to which can be applied the improved agar plate method of biotin bioassay. Assay characteristics were within acceptable ranges (intra-assay CVs, 4.44% and 1.95% at 1.82+/-0.08 and 3.08+/-0.06 pmol/min/ml; day-to-day CV, 5.92% at 2.68+/-0.16 pmol/min/ml). The enzyme activity with biocytin was stable at 4 degrees C for 90 days. The mean value of the serum biotinidase levels in 129 healthy adults was 2.71+/-0.93 pmol/min/ml. The method was clinically comparable with a colorimetric method for detection of biotinidase deficiency. Biotin supplementation treatment normalized our partial biotinidase deficiency patient's serum biotinidase activity. This normalized phenomenon has not yet been observed in a Caucasian patient. We also found that the distribution of the enzyme activities with biotinyl-p-aminobenzoate in 8 of 11 patients with suspected biotin metabolic disorders shifted to a higher level than that of the controls. Although, we have few opportunities to analyze the sera of biotin metabolic disorders in Japan, the new method are suitable for clinical research applications in combination with the colorimetric method.