Significant improvement from chronic beryllium disease following corticosteroid pulse therapy.

Chronic beryllium disease (CBD) is a rare disease characterized by diffuse interstitial pulmonary granulomatosis. We report a case of CBD which exhibited marked improvement both subjectively and objectively following pulse therapy. The patient was a 36-year-old man whose chief complaint was dyspnea and a dry cough. Since July 1990, the patient had been working in the development of an automatic or mechanical technique for producing beryllium-copper alloy. It appeared likely that the patient may have been exposed to metal beryllium fumes generated from an opening located just above the furnace. The Be concentration exceeded 25 microg/m3 transiently in the breathing zone in this workplace. A chest X-ray film taken in October 1994 showed fine granular shadows throughout the entire lung fields. Around August 1998, the patient's dyspnea became aggravated. An X-ray taken at that time showed linear and reticular shadows, in addition to the diffuse fine granular shadow. In October 1998, after 3 days of methylprednisolone pulse therapy, oral prednisolone 30 mg was initiated. With this treatment, the patient's pulmonary function tests and blood gases improved. Once the patient's condition had improved sufficiently, the dosage of prednisolone was decreased by 2.5 mg every two weeks. The patient continues to be monitored.

Molecular mechanism for pterin-mediated inactivation of tyrosine hydroxylase: formation of insoluble aggregates of tyrosine hydroxylase.

Tyrosine hydroxylase (TH), an iron-containing enzyme, catalyzes the first and rate-limiting step of catecholamine biosynthesis, and requires tetrahydrobiopterin (BH4) as a cofactor. We found that preincubation of recombinant human TH with BH4 results in the irreversible inactivation of the enzyme at a concentration far less than the Km value toward BH4 in spite of its cofactor role, whereas oxidized biopterin, which has no cofactor activity, does not affect the enzyme activity. We show that TH is inactivated by BH4 in competition with the binding of dopamine. The sequential addition of BH4 to TH results in a gradual decrease in the intensity of the fluorescence and CD spectra without changing their overall profiles. Sedimentation velocity analysis demonstrated an association of TH molecules with each other in the presence of BH4, and studies using gel-permeation chromatography, turbidity measurements, and transmission electron microscopy demonstrated the formation of amorphous aggregates with large molecular weights following the association of the TH proteins. These results suggest that BH4 not only acts as a cofactor, but also accelerates the aggregation of TH. We propose a novel mechanism for regulating the amount of TH protein, and discuss its physiological significance.

GTP cyclohydrolase I utilizes metal-free GTP as its substrate.

GTP cyclohydrolase I (GCH) is the rate-limiting enzyme for the synthesis of tetrahydrobiopterin and its activity is important in the regulation of monoamine neurotransmitters such as dopamine, norepinephrine and serotonin. We have studied the action of divalent cations on the enzyme activity of purified recombinant human GCH expressed in Escherichia coli. First, we showed that the enzyme activity is dependent on the concentration of Mg-free GTP. Inhibition of the enzyme activity by Mg2+, as well as by Mn2+, Co2+ or Zn2+, was due to the reduction of the availability of metal-free GTP substrate for the enzyme, when a divalent cation was present at a relatively high concentration with respect to GTP. We next examined the requirement of Zn2+ for enzyme activity by the use of a protein refolding assay, because the recombinant enzyme contained approximately one zinc atom per subunit of the decameric protein. Only when Zn2+ was present was the activity of the denatured enzyme effectively recovered by incubation with a chaperone protein. These are the first data demonstrating that GCH recognizes Mg-free GTP and requires Zn2+ for its catalytic activity. We suggest that the cellular concentration of divalent cations can modulate GCH activity, and thus tetrahydrobiopterin biosynthesis as well.