Biomedical subjects

L C Wood

Publications and source records attributed to L C Wood.

28 records · Page 2Linked to original sources

PubMed1988

Construction and characterization of mutant iso-2-cytochromes c with replacement of conserved prolines.

Oligonucleotide-directed mutagenesis has been used to construct two mutant forms of iso-2-cytochrome c. In one, Pro-30 is replaced by threonine; in the other, Pro-76 is replaced by glycine. Both prolines are fully conserved among mitochondrial cytochromes c and play important structural and functional roles. Yeast with either the Pro-30 or the Gly-76 mutation has appreciable levels of mutant protein in vivo and grows on media containing nonfermentable carbon sources. Thus, neither mutation blocks protein targeting to mitochondria, uptake by mitochondria, covalent attachment of heme, or in vivo function. As judged by ultraviolet-visible spectrophotometry and proton nuclear magnetic resonance spectroscopy, the nativelike conformation of purified Gly-76 iso-2 at pH 6 is almost indistinguishable from that of the normal protein at pH 6. Ultraviolet second-derivative spectrophotometry, however, suggests an increase in the average number of exposed tyrosine side chains, with 2.25 out of 5 residues exposed for the mutant compared to 1.95 for normal iso-2. Above neutral pH, the protein folds to a mutant conformation possibly related to alkaline cytochrome c. Nuclear Overhauser difference spectroscopy of the reduced nativelike conformation allows assignment of several proton resonances and comparison of side-chain conformations of the heme ligand Met-80 in the mutant and the normal proteins. The proton chemical shifts for the assigned resonances are the same within errors for Gly-76 iso-2 and normal iso-2 at pD 6, 20 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1988

Replacement of a conserved proline eliminates the absorbance-detected slow folding phase of iso-2-cytochrome c.

As a test of the proline isomerization model, we have used oligonucleotide site-directed mutagenesis to construct a mutant form of iso-2-cytochrome c in which proline-76 is replaced by glycine [Wood, L. C., Muthukrishnan, K., White, T. B., Ramdas, L., & Nall, B. T. (1988) Biochemistry (preceding paper in this issue)]. For the oxidized form of Gly-76 iso-2, an estimate of stability by guanidine hydrochloride induced unfolding indicates that the mutation destabilizes the protein by 1.2 kcal/mol under standard conditions of neutral pH and 20 degrees C (delta G degrees u = 3.8 kcal/mol for normal Pro-76 iso-2 versus 2.6 kcal/mol for Gly-76 iso-2). The kinetics of folding/unfolding have been monitored by fluorescence changes throughout the transition region using stopped-flow mixing. The rates for fast and slow fluorescence-detected refolding are unchanged, while fast unfolding is increased in rate 3-fold in the mutant protein compared to normal iso-2. A new kinetic phase in the 1-s time range is observed in fluorescence-detected unfolding of the mutant protein. The presence of the new phase is correlated with the presence of species with an altered folded conformation in the initial conditions, suggesting assignment of the phase to unfolding of this species. The fluorescence-detected and absorbance-detected slow folding phases have been monitored as a function of final pH by manual mixing between pH 5.5 and 8 (0.3 M guanidine hydrochloride, 20 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome c Group↗

PubMed1984

L-Thyroxine therapy in subclinical hypothyroidism. A double-blind, placebo-controlled trial.

The indications for treating patients with subclinical hypothyroidism (normal serum thyroxine and free thyroxine levels, but elevated serum thyrotrophin levels) are poorly defined. In this study, 33 patients with subclinical hypothyroidism were randomly assigned in a double-blind manner to receive placebo or L-thyroxine therapy and were followed for 1 year with thyroid function tests, serum lipid measurements, basal metabolic rate and systolic time interval determinations, and a questionnaire on hypothyroid symptoms. The placebo group showed no changes in thyroid function or peripheral indices of thyroid hormone action. In the thyroxine-treated group, serum lipids and the mean systolic time interval did not change, but the systolic time intervals became normal in the 5 patients with the most abnormal baseline values. Symptoms improved in 8 of 14 patients receiving thyroxine and in 3 of 12 patients receiving placebo (p less than 0.05). L-Thyroxine therapy may be useful for patients with subclinical hypothyroidism with abnormal myocardial contractility or symptoms consistent with mild hypothyroidism, or both.

Adult↗

PubMed1979

Hypothyroidism as a late sequela in patient with Graves' disease treated with antithyroid agents.

In 1971, thyroid function was evaluated in 15 unselected patients whose only therapy for diffuse toxic goiter was a course of thionamide drug treatment completed 20-27 yr earlier. One patient was frankly hypothyroid by clinical and laboratory criteria. The remaining 14 patients appeared clinically euthyroid and had a normal serum thyroxine (T(4)) concentration and thyroid radioiodine uptake (RAIU). Nevertheless, only 6 of 14 appeared to be entirely normal according to more refined criteria. The serum thyrotropin (TSH) concentration was markedly elevated in one patient and above the normal range (1.6+/-2.0; mean+/-2 SD) in five others. Thyroid stimulation with exogenous TSH revealed subnormal responses of the serum T(4)I, RAIU, or both, in 7 of 11 patients tested. An abnormal iodideperchlorate discharge test was found in 5 of 10 patients and appeared most abnormal in patients with abnormal RAIU responses to TSH. Fluorescent antimicrosomal antibody was found in the serum of 12 of the 15 patients, in contrast to an expected frequency of 7% in normal individuals of the same age. By the time a second major follow-up study was completed in 1978, two additional patients had become frankly hypothyroid. A third subject met accepted criteria for subclinical hypothyroidism. One of these subjects had had a clearly elevated serum TSH concentration in 1972, and the remaining two had exhibited the highest responses of serum TSH (36, 26 muU/ml) to thyrotropin-releasing hormone among 10 patients tested in 1972. One patient developed recurrent thyrotoxicosis in 1978, 25 yr after the onset of his first and only other apparent episode of hyperthyroidism. This patient was the only one who demonstrated a subnormal response to thyrotropin-releasing hormone in 1972. The remaining nine subjects that could be studied in 1978 exhibited varying combinations of abnormalities of thyroid function. It is concluded that progressive failure of thyroid function is a common occurence in long-standing Graves' disease, and it is suggested that this results from concomitant chronic thyroiditis. We postulate that this inherent tendency toward thyroid failure is exaggerated by surgery or radioactive iodine, explaining the progressive increase in, and inordinate frequency of, hypothyroidism after ablative modes of therapy in diffuse toxic goiter.

Adult↗

PubMed1975

Thyroid failure after potassium iodide treatment of diffuse toxic goiter.

1. The treatment of Graves' Disease by Potassium Iodide (like thyroidectomy, radioiodine, and antithyroid drugs) is followed by rate failure of thyroid function. 2. These findings suggest that the natural history of Graves' Disease may be one of progression from hyperthyroidism towards a decreased thyroid functional state. This progression may be accelerated by ablative methods of treatment. 3. Certainly, all patients with Graves' Disease, no matter what the treatment may be, should be followed carefully for the rest of their lives. 4. In certain patients, Potassium Iodide appears to be an effective means of controlling the hyperthyroidism of Graves' Disease.

Adult↗

PubMed1973