Involvement of histidine residues in catalytic activity of xanthine dehydrogenase from hen liver.

1. Modification of histidine residue(s) of xanthine dehydrogenase from hen liver by DEP and photooxidation results in loss of the ability to transfer electrons from xanthine to NAD+ and also from NADH to 2,6-dichlorophenolindophenol (DCIP). 2. The kinetics of inactivation suggest that carbethoxylation of more than one histidyl residue in the enzyme may be responsible for the inactivation.

Visual and brainstem auditory evoked potentials in hereditary motor-sensory neuropathy.

Visual evoked potentials (VEP) and brainstem auditory evoked potentials (BAEP) were recorded in 57 children and adults with hereditary motor-sensory neuropathy (HMSN); 37 of them were diagnosed as type I (demyelinating) and 20 as type II (axonal). None of the patients presented central nervous system involvement. The results were compared with VEP and BAEP records of 12 adults with Guillain-Barré syndrome (GBS) and 40 healthy controls. Above 30% of all patients with HMSN I showed delayed latency of the VEP. These abnormalities were less expressed in HMSN II. Abnormal BAEP were observed in almost 50% of patients with HMSN I and HMSN II with nearly the same frequency in both types but more pronounced in HMSN I. The most common feature was prolongation of the I-III interpeak latency (JPL). The VEP and BAEP changes could be present simultaneously in the same patient (mainly in HMSN I) or separately. More often the abnormalities were observed in the adult patients. Normal VEP and BAEP values were present in all patients with GBS. The results strongly suggest the subclinical optical and auditory pathways involvement in HMSN patients.

Comparison of xanthine:NAD+ oxidoreductase from liver of two uricotelic species: hen Gallus gallus and snake Natrix natrix.

1. Kinetic properties of xanthine:NAD+ oxidoreductase from liver of two uricotelic species of vertebrates (hen Gallus gallus and snake Natrix natrix) are compared. 2. Hen enzyme is saturated by hypoxanthine and xanthine at higher concentrations than the snake enzyme. For both species the enzyme-saturating concentration and hydroxylation rate of hypoxanthine are higher than those of xanthine, and the rate of uric acid production in the hypoxanthine----xanthine----uric acid reaction sequence is independent of the initial hypoxanthine concentration. 3. Km's for xanthine are the same, but Km for NAD+ of the hen enzyme is approximately 5-fold lower. The enzyme from both species is inhibited by NADH only slightly and at high non-physiological concentrations.

Xanthine:NAD+ oxidoreductase from embryo liver of hen Gallus gallus.

1. Xanthine:NAD+ oxidoreductase from chick embryo liver is unconvertible to the O2-dependent form, as is the enzyme from the adult hen. The Km for NAD+ (approximately 3 microM) of the embryonic enzyme is equal to, and the Km for xanthine (approximately 5 microM) is 2.5-fold lower, when compared with respective Km values of the "adult" hen enzyme. The inhibition of embryonic enzyme by NADH begins at 10 microM NADH and attains 13% at 35 microM NADH (respective data for the "adult" enzyme: 50 microM and 20% at 80 microM NADH). 2. The course of hypoxanthine----xanthine----uric acid hydroxylation catalyzed by the embryonic and "adult" enzymes is similar, however the rate of the first reaction is 2-fold lower for the embryonic enzyme. Under conditions of the limited nutritional system in the developing chick embryo, the low rate of hypoxanthine hydroxylation may promote reutilization of hypoxanthine for nucleotide synthesis.

Comparison of xanthine: NAD+ oxidoreductase from liver of toad Bufo viridis and other vertebrates.

1. Xanthine oxidoreductase was isolated from toad Bufo viridis (a mainly ureotelic amphibian species) and partially purified. The enzyme occurred as a stable xanthine: NAD+ oxidoreductase (EC 1.1.1.204), unconvertible to the oxidase form. 2. Some properties of the enzyme resembled those of xanthine oxidoreductase from an ammonotelic fish, Cyprinus carpio, and the ureotelic rat, but in other aspects it was similar to this enzyme from an uricotelic snake, Natrix natrix. 3. Inhibition of the toad enzyme by NADH at high non-physiological concentrations rules out a modulation of its oxypurine-hydroxylating activity by in vivo changes in the NADH/NAD+ ratio. Therefore, toad xanthine oxidoreductase plays no regulatory role in the purine nucleotide metabolism.

Two distinct types of mutations conferring to Escherichia coli K12 capability of D-tryptophan utilization.

We showed that the ability of Escherichia coli K12 tryptophan auxotrophs to utilize D-tryptophan as a substitute for L-tryptophan may result from two types of mutations. The first type consisted in changes in the dadR regulatory site of the dad operon increasing the synthesis of D-amino acid dehydrogenase. The mutations of the second type mapped within the dad A structural gene. They changed the apparent substrate specificity of D-amino acid dehydrogenase. We suppose that the change may be due to an altered enzyme structure which make it more accessible to D-tryptophan.