BIOTINYLATION OF HISTONES BY HUMAN SERUM BIOTINIDASE - ASSESSMENT OF BIOTINYL-TRANSFERASE ACTIVITY IN SERA FROM NORMAL INDIVIDUALS AND CHILDREN WITH BIOTINIDASE DEFICIENCY

Serum biotinidase has biotinyl-transferase activity in addition to bio cytin hydrolase activity. A sensitive assay for biotinyl-transferase a ctivity was developed based on the transfer of biotin from biocytin to histones. Biotinidase biotinyl-transferase occurs at physiological an d alkaline pHs, whereas hydrolysis of biocytin occurs optimally at pH 4.5 to 6.0. Measurement of hydrolysis requires micromolar concentratio ns of biocytin, whereas biotinylation of histones can be detected read ily at 1.5 nM biocytin. Because polylysine is readily biotinylated by biotinidase in the presence of biocytin, whereas polyarginine is not, the enzyme likely transfers biotin to the E-amino group of lysyl resid ues. To determine if patients who are deficient in biocytin hydrolase activity are also deficient in biotinyl-transferase activity, serum fr om 103 children (25 identified by exhibiting clinical symptoms and 78 detected by newborn screening) with profound biotinidase deficiency (l ess than 10% of mean normal biotinyl-p-aminobenzoate hydrolyzing activ ity) were assessed for biotinyl-transferase activity and for the prese nce of cross-reacting material (CRM) to antibodies prepared against pu rified serum biotinidase. Sera from all symptomatic: patients, both CR M-negative and CRM-positive, had no biotinyI-transferase activity. Ser a that was CRM-negative from children ascertained by newborn screening also had no biotinyl-transferase activity, whereas sera from 67% of t he CRM-positive children identified by newborn screening had varying d egrees of biotinyl-transferase activity. These results indicate that t here is a large group of enzyme-deficient children detected by newborn screening who are different biochemically fi om those who are symptom atic. The clinical relevance of having some degree of biotinyl-transfe rase activity for individuals with biotinidase deficiency remains to b e determined. In addition, it is important to determine if biotinyl-tr ansferase activity, especially biotinylation of histones, is a physiol ogical function of biotinidase. (C) 1995 Academic Press Inc.