Carboxylases biotinidase

Biotinidase (EC 3.5.1.12) is required for the recycling of biotin and for the utilization of protein bound biotin from the diet. Biotin (vitamin H) functions as a prosthetic group of four carboxylases in man the mitochondrial propionyl-CoA carboxylase,... 

It is important to note that normal plasma biotinidase activity does not exclude that the patient has another cause of multiple carboxylase deficiency (i.e. HCS deficiency or acquired biotin deficiency) [2, 30]. 

Wolf B, Grier RE, Allen RJ, Goodman SI, Kien CL (1983) Biotinidase deficiency the enzymatic defect in late-onset multiple carboxylase deficiency. Clin Chim Acta 131 273-281... 

Biotin is a cofactor of various carboxylases, but its effectiveness in pyruvate carboxylase deficiency is unproven. However, it has been used effectively in cases of biotinidase deficiency, a vary rare cause of congenital lactic acidosis. 

To determine the type of multiple carboxylase deficiency, blood was obtained to determine the biotin holocarboxylase synthetase activity in leukocytes, and serum was sent to determine the biotinidase activity. The results of the serum biotinidase activity returned first and indicated less than 1% of mean normal serum activity, confirming that the child had profound biotinidase deficiency (less than 10% of mean normal serum biotinidase activity). Subsequently, biotin holocarboxylase synthetase activity was found to be normal. Although many states screen for biotinidase deficiency in the newborn period, this child was bom in a state where newborn screening for biotinidase deficiency is not performed. 

Figure 12-2. Metabolic pathways involving the four biotin-dependent carboxylases. The solid rectangular blocks indicate the locations of the enzymes ACC, acetyl-CoA carboxylase PMCC, P-methylcrotonyl-CoA carboxylase PC, pyruvate carboxylase PCC, propionyl-CoA carboxylase. Isolated deficiencies of the first three carboxylases (mitochondrial) have been established (isolated ACC deficiency has not been confirmed). At least the activities of the three mitochondrial carboxylases can be secondarily deficient in the untreated multiple carboxylase deficiencies, biotin holocarboxylase synthetase deficiency and biotinidase deficiency. Lowercase characters indicate metabolites that are frequently found at elevated concentrations in urine of children with both multiple carboxylase deficiencies. The isolated deficiencies have elevations of those metabolites directly related to their respective enzyme deficiency.

Urinary organic acid analysis is useful for differentiating isolated carboxylase deficiencies from the biotin-responsive multiple carboxylase deficiencies. P-Hydroxyisovalerate is the most common urinary metabolite observed in isolated P-methylcrotonyl-CoA carboxylase deficiency, biotinidase deficiency, biotin holo-carboxylase synthetase deficiency, and acquired biotin deficiency. In addition to P-hydroxy-isovalerate, elevated concentrations of urinary lactate, methylcitrate, and P-hydroxypropionate are indicative of multiple carboxylase deficiency. 

Both multiple carboxylase deficiencies are characterized by deficient activities of the three mitochondrial carboxylases in peripheral blood leukocytes prior to biotin treatment. The carboxylase activities increase to near normal or normal after treatment with pharmacological doses of biotin. Patients with biotin holocarboxylase synthetase deficiency have deficient activities of the three mitochondrial carboxylases in fibroblasts incubated in medium with low biotin concentrations (containing only the biotin contributed by fetal calf serum added to the medium for cell growth), whereas patients with biotinidase deficiency have normal carboxylase activities under these conditions. The activities of the carboxylases in biotin holocarboxylase synthetase deficiency become near normal to normal when cultured in medium supplemented with high concentrations of biotin. 

Biotinidase deficiency and biotin holocarboxylase synthetase deficiency can be definitively diagnosed by direct enzymatic assay. Biotinidase activity in plasma or serum is usually determined by using the artificial substrate, biotinyLp-aminobenz< >ate. If biotinidase activity is present, then biotin is cleaved, releasing jD-aminobenzoatc. The / -aminobenzoate then is reacted with reagents that result in the development of purple color that can be quantitated colorimetrically. In the absence of biotinidase activity,/ -aminobenzoate is not liberated. Biotinidase activity in patients with an isolated carboxylase deficiency or biotin holocarboxylase synthetase deficiency is normal. 

Figure 12-4. The biotin cycle shows the actions of biotin holocarboxylase synthetase in biotinylating carboxylases and of biotinidase in cleaving biocytin, thereby recycling biotin.

Two children with the late-onset form initially were reported as having a defect in intestinal transport of biotin. This conclusion was supported by finding low plasma biotin concentrations when these children were administered oral biotin compared to the concentrations of plasma biotin of unaffected control subject. In 1983, it was demonstrated that the primary biochemical defect in most patients with late-onset multiple carboxylase deficiency was a deficiency of serum biotinidase activity. The two children with a putative defect in intestinal biotin transport both were confirmed to have biotinidase deficiency. This disparity was reconciled by demonstrating that, in both cases, the children were biotin depleted at the time the biotin-loading studies were performed. Therefore, when the children initially were given biotin, although the vitamin was transported into the blood normally, it was rapidly taken up... 

Individuals with untreated biotinidase deficiency develop biotin deficiency because they cannot recycle endogenous biotin. The biotin deficiency subsequently results in the lack of substrate for biotin holocarboxylase synthetase. Without the availability of biotin to be added to the apocarboxylases, multiple carboxylase deficiency occurs, and the abnormal metabolites accumulate. 

The mainstay of therapy in biotinidase deficiency is biotin supplementation. To date, all symptomatic children with biotinidase deficiency have improved after treatment with 5 to 10 mg of biotin per day. Biotin appears to be required in the free form as opposed to the bound form. This is based on the findings of two children who were fed yeast as a form of therapy. Neither improved because essentially all of the biotin in yeast is protein bound, and these children could not recycle the biotin. These children, however, did improve when treated with free biotin. Treatment with biotin is essential and sufficient to prevent or resolve the symptoms. It is not necessary to treat children with biotinidase deficiency with protein-restricted diets as it is in some of the isolated carboxylase deficiencies because with biotin therapy all the carboxylase activities are normal. Symptoms of biotinidase deficiency are preventable if patients are diagnosed and treated at birth or before symptoms occur. 

Table 11.1 Abnormal Urinary Organic Acids in Biotin Deficiency and Multiple Carboxylase Deficiency from Lack of Holocarboxylase Synthetase or Biotinidase...

Biotinidase Deficiency Genetic lack of biotinidase results in the late-onset variant of multiple carboxylase deficiency. Patients generally present later in life than those with holocarboxylase synthetase deficiency (Section 11.2.2.1) and have a lower than normal blood concentration of biotin. Culture of fibroblasts in media containing low concentrations of biotin results in normal activities of carboxylases, and holocarboxylase synthetase activity is normal. 

Biotin deficiency and the functional deficiency associated with lack of holo-carboxylase synthetase (Section 11.2.2.1), or biotinidase (Section 11.2.3.1), causes alopecia (hair loss) and a scaly erythematous dermatitis, especially around the body orifices. The dermatitis is similar to that seen in zinc and essential fatty acid deficiency and is commonly associated with Candida albicans infection. Histology of the skin shows an absence of sebaceous glands and atrophy of the hair follicles. The dermatitis is because of impaired metabolism of polyunsaturated fatty acids as a result of low activity of acetyl CoA carboxylase (Section 11.2.1.1). In biotin-deficient experimental animals, provision of supplements of long-chain 6 polyunsaturated fatty acids prevents the development of skin lesions (Mock et al., 1988a, 1988b Mock, 1991). 

Proteolysis of biotin-containing enzymes releases -biotinyllysine, or biocytin. Biotinidase cleaves biocytin and biotinylated peptides, resulting from degradation of endogenous carboxylases, to biotin and lysine. Thus,... 

Biotinidase deficiency Folinic acid-responsive seizures Glutaric aciduria type 1 Homocystinuria HyperphenyManinemia due to disorders of biopterin Methylmalonic aciduria Maple syrup urine disease (MSUD) Multiple carboxylase deficiency OAT... 

Proteolytic degradation of holocarboxylases leads to the formation of bio-tinyl peptides and biocytin (biotin-8-lysine). These compounds are further degraded by biotinidase to release biotin, which is then recycled in holo-carboxylase synthesis (Wolf et al. 1985). 

Breakdown of carboxylases leads to the release of biotinylated polypeptides. Biotinidase releases free biotin from these peptides for recycling in the synthesis of new holocarboxylases (cf. biotinidase deficiency by Wolf and Heard 1991). In the 1990s, biotinidase was considered the enzyme that might be responsible for mediating the binding of biotin to histones (Hymes et al. 1995). Clearly, biotinidase has catalytic activity to mediate biotinylation of histones in vitro (Camporeale et al. 2004). However, evidence suggests that HLCS is the enzyme that mediates biotinylation of histones in vivo (Camporeale et al. 2006) and that biotinidase might play a role in the enzymatic removal of biotin from histones (Ballard et al. 2002), which is consistent with their roles in carboxylase metabolism. 

Holocarboxylase synthetase catalyses the covalent binding of biotin to carboxylases, whereas biotinidase catalyses the release of free biotin from degraded carboxylases. 

For biotin coming from endogenous biotinyl proteins, biotin-containing carboxylases are degraded to biotinyl peptides which leads to the formation of biocytin through sequential hydrolysis. The intervention of biotinidase releases lysine and biotin. 

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