Comparative aspects of hydroxamic acid production by thiamine-dependent enzymes

The reactions of 4-chloronitrosobenzene with pyruvate decarboxylase and transketolase were investigated by use of a new high-pressure liquid chromatography method to determine any differences between these two enzymes with respect to hydroxamic acid production. In addition to the previously established difference in the type of hydroxamic acid produced by the two enzymes, several new and interesting differences in their reaction with nitrosoaromatics were discovered. Most notable was the finding that pyruvate decarboxylase gave 4-chlorophenylhydroxylamine as the major product from 4-chloronitrosobenzene, while transketolase did not produce any detectable hydroxylamine. A redox mechanism was proposed to account for arylhydroxylamine production by pyruvate decarboxylase. This redox mechanism can also explain hydroxamic acid production by pyruvate decarboxylase; however, a previously proposed nucleophilic reaction mechanism occurring simultaneously could not be totally disproven. Either of the two mechanisms is equally likely for transktolase action in view of the present evidence. Another major difference between these enzymes is that the rate of 4-chloronitrosobenzene conversion was found to be much faster for pyruvate decarboxylase than for transketolase when each enzyme was subjected to its own optimal reaction conditions. Transketolase displayed typical enzyme saturation kinetics with 4-chloronitrosobenzene with a K_m of 0.31 mM and V_max of 0.033 μmol ml^?1 min^?1 unit^?1 relative to 5 mMd-fructose 6-phosphate as sugar substrate. On the other hand, the reaction with pyruvate decarboxylase was first order in 4-chloronitrosobenzene with a combined rate constant of 2.0 min^?1 unit^?1 ml.     

Unsaturated fatty acid-dependent oxidation of epinephrine in homogenates of the gorgonian, Pseudoplexaura porosa

A novel epinephrine oxidation system in homogenates of the gorgonian Pseudoplexaura porosa was discovered. The enzymatic reaction required an unsaturated fatty acid and molecular oxygen or hydrogen peroxide. Diphenylisobenzofuran was also oxidized by Ps. porosa homogenates in the presence of an unsaturated fatty acid. Hydroxyl radical and superoxide anion did not appear to be involved in either of these oxidative reactions. The production of lipid hydroperoxides was not necessary for epinephrine oxidation and, with the exception of arachidonic acid, lipid hydroperoxide production did not occur. Evidence is presented for the involvement of singlet oxygen or a similar activated oxygen intermediate in the reactions, and a possible mechanism was proposed. The use of arachidonate-dependent epinephrine oxidation as a measure of prostaglandin synthetase activity is criticized.     

Peroxide oxidation of indole to oxindole by chloroperoxidase catalysis.

In the presence of chloroperoxidase, indole was oxidized by H2O2 to give oxindole as the major product. Under most conditions oxindole was the only product formed, and under optimal conditions the conversion was quantitative. This reaction displayed maximal activity at pH 4.6, although appreciable activity was observed throughout the entire pH range investigated, namely pH 2.5-6.0. Enzyme saturation by indole could not be demonstrated, up to the limit of indole solubility in the buffer. The oxidation kinetics were first-order with respect to indole up to 8 mM, which was the highest concentration of indole that could be investigated. On the other hand, 2-methylindole was not affected by H2O2 and chloroperoxidase, but was a strong inhibitor of indole oxidation. The isomer 1-methylindole was a poor substrate for chloroperoxidase oxidation, and a weak inhibitor of indole oxidation. These results suggest the possibility that chloroperoxidase oxidation of the carbon atom adjacent to the nitrogen atom in part results from hydrogen-bonding of the substrate N-H group to the enzyme active site.     

The amino acid sequence of chick skin collagen α1-CB7: The presence of a previously unrecognized triplet

Because alignment of the amino acid sequences of chick skin collagen α2-CB3 (1) with the relevant portion of chick skin collagen α1-CB7 (2) suggested that a Gly-X-Y triplet may have been missed in the latter, the peptide TM-2, produced by tryptic digestion of maleylated α1-CB7, was reinvestigated. Cleavage by trypsin at the unblocked lysine at position 18, and isolation of the resulting COOH-terminal peptide, showed this to be a 15-residue peptide containing a previously unrecognized Gly-Pro-Hyp triplet. Sequencing of the peptide showed this to occupy positions 4 through 6, or 56 through 58 of α1-CB7. The latter thus has 271 instead of 268 residues, and the α1[I] chain 1055 instead of 1052.     

Prognostic value of early features in rheumatoid disease.

Extensive data on 102 patients who presented with rheumatoid disease within a year of onset were gathered by a prospective study to assess the prognostic value of early features. Outcome was evaluated at a mean 4-5 years from onset on the basis of functional grade, extent of joint disease, early morning stiffness, and grip strength. Twenty-six patients improved, 14 pursued a mild steady course, and 62 had a persistently severe or deteriorating condition. The features recorded at the first visit were correlated with outcome. Those indicating a poor prognosis were: older age at onset, being underweight, poor grip strength, many affected joints, involvement of wrist or metatarsophalangeal joints, poor functional status, fulfilment of many of the American Rheumatism Association criteria for rheumatoid disease, raised erythrocyte sedimentation rate, seropositivity on sheep cell agglutination or latex tests, low haemoglobin level, raised blood urea level, and early erosions on x-ray films.     

Insulin stimulation of heart glycogen synthase D phosphatase (protein phosphatase).

Insulin rapidly produced an increase in per cent of total heart glycogen synthase in the I form in fed rats. In fasted rats the response was diminished and delayed. In diabetic animals there was no response over the 15-min time period studied. Since synthase phosphatase activity is necessary for synthase D to I conversion, the phosphatase activity was determined in extracts from these groups of animals. In the fasted and diabetic rats phosphatase activity was less than one-half of that in fed animals. Administration of insulin to fasting animals increased synthase phosphatase activity to a level approaching that of fed animals by 15 min. In diabetic animals insulin also stimulated an increase in synthase phosphatase activity but 30 min were required for full activation. Insulin had no effect in normal fed animals. Insulin activation of synthase phosphatase activity in heart extracts from fasted animals was still present after Sephadex G-25 chromatography and ammonium sulfate precipitation. Thus insulin had induced a stable modification of the phosphatase itself or of its substrate synthase D rendering the latter a more favorable substrate for the reaction. A difference in sensitivity of the reaction to glycogen inhibition was present between fed and fasted animals. Increasing concentrations of glycogen had only a slight inhibitory effect in extracts from fed animals but considerably reduced activity in extracts from fasted animals. Insulin administration reduced the sensitivity of the phosphatase reaction to glycogen inhibition. This could explain, at least in part, the increased phosphatase activity noted in the insulin-treated, fasted rats since glycogen was routinely added to the homogenizing buffer.     

Serum ferritin,cobalt excretion and body iron status.

Serum ferritin concentration was measured by immunoradiometric assay in 64 subjects. It was closely related to the size of body iron stores measured by hemosiderin content of bone marrow in all subjects and by the deferoxamine test in 10 patients with iron overload. Urinary cobalt excretion, an indirect measure of iron absorption, was inversely related to hemosiderin content of bone marrow in 34 patients aged 18 to 72 with or without liver disease, but this relation did not hold in a group of 20 student volunteers aged 17 to 30, indicating that the test is unreliable in young people. A strong inverse correlation was demonstrated between values for cobalt excretion and serum ferritin in the 34 patients and between those for iron absorption and serum ferritin in the 20 students. Serum ferritin concentration appears to reflect accurately the iron status of the healthy individual but high values in liver disease must be interpreted with caution.