Biotinidase (EC 3.5.1.12) catalyzes the hydrolysis of
biocytin, the product of
biotin-dependent carboxylase degradation, to
biotin and
lysine.
Biotinidase deficiency is an inherited metabolic disorder of
biotin recycling that is characterized by neurological and cutaneous abnormalities, and can be successfully treated with
biotin supplementation. Sequences of tryptic
peptides of the purified human serum
enzyme were used to design
oligonucleotide primers for polymerase chain reaction amplification from human hepatic total
RNA to generate putative
biotinidase cDNA fragments. Sequence analysis of a
cDNA isolated from a human liver library by plaque hybridization with the largest
cDNA probe revealed an open reading frame of 1629 bases encoding a
protein of 543
amino acid residues, including 41
amino acids of a potential
signal peptide. Comparison of the open reading frame with the known
biotinidase tryptic
peptides and recognition of the expressed
protein encoded by this
cDNA by
monoclonal antibodies prepared against purified
biotinidase demonstrated the identity of this
cDNA. Southern analyses suggested that
biotinidase is a single copy gene and revealed that human
cDNA probes hybridized to genomic
DNA from mammals, but not from chicken or yeast. Northern analysis indicated the presence of
biotinidase mRNA in human heart, brain, placenta, liver, lung, skeletal muscle, kidney, and pancreas.