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Biomedical subjects

R Park

Publications and source records attributed to R Park.

At least 109 records · Page 6Linked to original sources
PubMed1980

Lactic acidosis.

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Acid-Base Equilibrium↗
PubMed1980

Lactic acidosis.

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Acidosis↗
PubMed1979

REM sleep episodes during the Multple Sleep Latency Test in narcoleptic patients.

Forty narcoleptic patients were given the Multiple Sleep Latency Test, consisting of 20 min opportunities to sleep offered at 10.00, 12.00, 14.00, 16.00 and 18.00 o'clock. Eleven patients had 2 episodes of REM sleep, 5 had 3, 11 had 4, and 13 had 5 before they were awakened. Fourteen control subjects given similar opportunities to sleep (reported in a companion article (Richardson et al. 1978)) had no REM sleep episodes. For the 10.00-18.00 o'clock opportunities respectively, there were 32, 29, 30, 28 and 27 REM sleep episodes. We conclude that this procedure can provide physicians with data useful in the diagnosis of narcolepsy.

Adult↗
PubMed1979

Determination of liver intracellular pH in vivo and its homeostasis in acute acidosis and alkalosis.

An in vivo method is presented for the determination of liver intracellular pH (pHi) using [14C]dimethadione (DMO) in dogs. This method differs from those previously published in that hepatic venous and portal venous blood pH were selected as the extracellular reference pH, and liver blood space corrections are applied to whole liver tissue [14C]DMO activity. Using these corrections, a normal liver pHi of 6.99 +/- 0.03 (SE) was obtained. During acute metabolic acidosis and alkalosis, as well as during acute respiratory acidosis and alkalosis, the liver pHi remained normal; metabolic acidosis was 7.04 +/- 0.04; metabolic alkalosis was 6.92 +/- 0.08; respiratory acidosis was 6.98 +/- 0.04; and respiratory alkalosis was 7.00 +/- 0.10. None of these values was significantly different from normal (P greater than 0.05). Changes in intracellular bicarbonate and lactate appeared to account in part for the observed stability of the liver pHi despite acute manipulations resulting in a range of pH values between 7.09 and 7.63 in arterial blood.

Acid-Base Imbalance↗
PubMed1978

Allosteric regulation of monocyclic interconvertible enzyme cascade systems: use of Escherichia coli glutamine synthetase as an experimental model.

The interconversion of Escherichia coli glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] between its adenylylated and unadenylylated forms has been used to verify the prediction derived from a theoretical analysis of the steady-state functions of a model for a monocyclic interconvertible enzyme cascade system [Stadtman, E. R. & Chock, P. B. (1977) Proc. Natl. Acad. Sci. USA 74, 2761-2770]. Because glutamine and alpha-ketoglutarate are multifunctional effectors and because three active enzyme complexes are involved in both adenylylation and deadenylylation of glutamine synthetase, at least 28 constants are required to describe the glutamine synthetase monocyclic cascade. Of these, 22 constants were determined experimentally and 6 were estimated via computer curve fitting. Despite the complexity, when both adenylylation and deadenylylation reactions are functioning, the number of adenylyl groups bound per mole of enzyme, n, assumes a steady-state level as is predicted by the model. This n value is determined by the mole fraction of P(IIA)-given by ([P(IIA)]/([P(IIA)] + [P(IID)])-and the ratio of glutamine to alpha-ketoglutarate (P(IID) and P(IID) are the unmodified and the uridylylated forms of the P(II) regulatory protein). In the presence of 0.5 mM glutamine and 2 mM alpha-ketoglutarate, the value of n increases as a nearly hyperbolic function in response to increasing mole fractions of P(IIA). When the constant level of alpha-ketoglutarate is gradually increased to 40 muM, the hyperbolic function converts slowly to a parabolic function. When the P(IIA) mole fraction was maintained at 0.6 and alpha-ketoglutarate levels were varied from 1 mM to 4 muM, an 800-fold increase in signal amplification was observed with respect to glutamine activation. In addition, because glutamine activates the adenylylation and inhibits the deadenylylation reaction, a sensitivity index of 2.1 (corresponding to a Hill number of 1.5) was obtained for the variation of n values in response to increasing glutamine concentration.

Adenosine Monophosphate↗
PubMed1977

Polypeptide composition of chlorophyll-protein complexes from romaine lettuce.

The protein moiety of the two major chlorophyll-protein complexes associated with chloroplast membranes of outer, dark green leaves of a romaine lettuce shoot (Lactuca sativa L. var. Romana) has been analyzed by discontinuous sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Complex II, also termed light-harvesting chlorophyll-protein complex, is shown to consist of a major polypeptide of 25 kilodaltons (kD) and two minor ones of 27.5 and 23 kD. The 25 kD subunit is the single largest polypeptide component of the chloroplast membranes, accounting for about 25% of their total protein. Complex I contains only high molecular weight subunits, the major one being at 67 kD, these subunits representing only a small percentage of the chloroplast membrane total protein.These data, suggesting an oligomeric nature for the apoprotein of these two chlorophyll-protein complexes, are difficult to reconcile with the estimated molecular weights of the native complexes and raise some intriguing questions as to the types of interactions among the components of these major lipoproteins of the photosynthetic membranes.

Journal Article↗
PubMed1977

Chemotherapy for mustard-resistant ovarian adenocarcinoma: a randomized trial for CCNU and methyl-CCNU.

In view of the need for drugs which have antitumor activity in alkylating agent-resistant ovarian cancer or which might be more potent than standard agents, a randomized trial of two nitrosoureas, CCNU and methyl-CCNU, has been conducted. Of 31 evaluable patients who received at least one dose of CCNU (100 mg/m2 orally every 6 weeks), there were only two patients who experienced even transient improvement; 18 of these patients had two or more doses over a trial period of greater than or equal to 12 weeks. Of 26 evaluable patients who received at least one dose of methyl-CCNU (150 mg/m2 orally every 6 weeks), there was one patient who experienced transient improvement; this group included 14 patients receiving at least two doses and whose trial lasted greater than or equal 12 weeks. All patients had been previously treated with mustard-type alkylating agents. None of the responses were clinically useful. Thus, women with ovarian adenocarcinoma who have a history of prior chemotherapy are not likely to benefit from treatment with these nitrosoureas.

Adenocarcinoma↗
PubMed1975

Treatment of squamous cell carcinoma involving the buccal pouch in a crab-eating macaque.

Persistent swelling of the left buccal pouch was noticed in an adult female crab-eating macaque (Macaca fascicularis). A mass involving almost the entire musculature of the pouch was removed surgically. The histopahtologic diagnosis was squamous cell carcinoma. Recurrence of the mass was treated by a combination of surgical excision and radiation therapy.

Animals↗
PubMed1975

Stomach and upper intestine of the rat in the regulation of food intake.

The role of the upper intestine in the regulation of food intake and gastric emptying has been studied in normal, gastrectomized, and "crossover" rats, parabiotic rats with a common visceral cavity in which the proximal duodenum of each parabiont is anastomosed to the pylorus of the stomach of the partner. One rat of "crossover" pairs eats and the partner eats little or nothing. Normal rats fed a raw soybean (RS) diet ate less and gastric evacuation proceeded more slowly than in normal rats fed a heated soybean (HS) diet. It is postulated that RS contains a heat-labile intestinal irritant. The upper intestine of gastrectomized rats regulates food intake and prevents overloading of the intestine. Force feeding of excessive amounts of the RS diet elicited the secretion of much more solids and nitrogen into the upper intestine than did similar amounts of the HS diet. The upper intestines of "crossover" rats lose all control over entry of gastric contents into their duodena. Fed ad libitum, the parabiont whose stomach emptied first, ate continuously, while the recipient partner showed diarrhea. It is postulated that the control of food intake traditionally assigned to the stomach resides, rather, in the upper intestine.

Animals↗
PubMed1975

High resolution gel electrophoresis of chloroplast membrane polypeptides.

In the present study we extend previous work from this laboratory on the polypeptide composition of photosynthetic lamellae. Using a high resolution sodium dodecyl sulfate gel electrophoresis technique, we show that both grana and stroma lamellae have qualitatively very similar polypeptide compositions although some clear quantitative differences are demonstrated.

Journal Article↗
PubMed1974

Biosynthesis of grana and stroma lamellae in spinach.

Park and co-workers (Annu. Rev. Plant Physiol. 22: 395-430) have suggested that stroma lamellae, which perform only photosystem I contain a developing photosystem II which becomes functional upon the folding of these membranes to form grana stacks.The present study was undertaken to test this hypothesis. The lipid and protein constituents of chloroplast membranes were pulse-labeled radioactively with (14)C, and the specific activity of stroma and grana components were studied in a pulse-chase experiment. The components of both grana and stroma lamellae become labeled and decay at similar rates which suggests that the Park and Sane hypothesis is not correct. The results also show large differences in the turnover rates of some chloroplast membrane components supporting the multistep model for membrane synthesis and maintenance in this organelle.

Journal Article↗