Omental torsion: CT features.

A 33-year-old male presented to the emergency department complaining of right upper quadrant pain and was initially diagnosed with acute cholecystitis. Abdominal computed tomography showed a whirling pattern of fatty streaks and vessels within the greater omentum, and surgery confirmed infarction of the omentum secondary to torsion. We report a case of surgically and pathologically proven omental torsion that demonstrated the typical whirling appearance on computed tomography.

Comparison of peroxidase reaction mechanisms of prostaglandin H synthase-1 containing heme and mangano protoporphyrin IX.

Prostaglandin H synthase (PGHS) is a heme protein that catalyzes both the cyclooxygenase and peroxidase reactions needed to produce prostaglandins G2 and H2 from arachidonic acid. Replacement of the heme group by mangano protoporphyrin IX largely preserves the cyclooxygenase activity, but lowers the steady-state peroxidase activity by 25-fold. Thus, mangano protoporphyrin IX serves as a useful tool to evaluate the function of the heme in PGHS. A detailed kinetic analysis of the peroxidase reaction using 15-hydroperoxyeicosatetraenoic acid (15-HPETE), EtOOH, and other peroxides as substrates has been carried out to compare the characteristics of PGHS reconstituted with mangano protoporphyrin IX (Mn-PGHS) to those of the native heme enzyme (Fe-PGHS). The rate constant describing the reaction of Mn-PGHS with 15-HPETE to form the oxidized, Mn(IV) intermediate with absorption at 420 nm, exhibits saturable behavior as the 15-HPETE concentration is raised from 10 to 400 microM. This is most likely due to the presence of a second, earlier intermediate between the resting enzyme and the Mn(IV) species. Measurements at high substrate concentrations permitted resolution of the absorbance spectra of the two oxidized Mn-PGHS intermediates. The spectrum of the initial intermediate, assigned to a Mn(V) species, had a line shape similar to that of the later intermediate, assigned to a Mn(IV) species, suggesting that a porphyrin pi-cation radical is not generated in the peroxidase reaction of Mn-PGHS. The rate constant estimated for the formation of the earlier intermediate with 15-HPETE is 1.0 x 10(6) M-1 s-1 (20 degrees C, pH 7.3). A rate constant of 400 +/- 100 s-1 was estimated for the second step in the reaction. Thus, Mn-PGHS reacts considerably more slowly than Fe-PGHS with 15-HPETE to form the first high-valent intermediate, but the two enzymes appear to follow a similar overall reaction mechanism for generation of oxidized intermediates. The difference in rate constants explains the observed lower steady-state peroxidase activity of Mn-PGHS compared with Fe-PGHS.

High-valent intermediates in the reaction of N alpha-acetyl microperoxidase-8 with hydrogen peroxide: models for compounds 0, I and II of horseradish peroxidase.

N-acetyl microperoxidase-8 (Ac-MP-8) is a water soluble, ferric heme model for the peroxidases. The reaction of Ac-MP-8 with H2O2 in 10 mM potassium phosphate over the pH range of 7-11 gives rise sequentially to relatively stable green and red species with properties that closely mimic those of HRP compounds I and II, respectively. Low-temperature stopped-flow studies of this reaction carried out in 50% v/v methanol/10 mM potassium phosphate, pH* 9.1 at -25.8 degrees C indicate that the pseudo-first-order rate constant, kobs, that describes the formation of the green intermediate exhibits saturation kinetics as a function of [H2O2] with kmaxobs = 95 s-1 and KM = 87 mM. Rapid-scan studies carried out with [H2O2] = 200 mM at -38.0 degrees C show that a compound 0 species with a characteristic band near 340 nm is formed whose conversion to the green species is rate limiting. Thus, Ac-MP-8 has high-valent forms that are models for all three known intermediates in the peroxidase cycle of horseradish peroxidase.

Construction of a fast, inexpensive rapid-scanning diode-array detector and spectrometer.

A 512-element diode-array spectroscopic detection system capable of acquiring multiple spectra at a rate of 5 ms per spectrum with an effective scan rate of 102.9 kHz has been constructed. Spectra with fewer diode elements can also be acquired at scan rates up to 128 kHz. The detector utilizes a Hamamatsu silicon photodiode-array sensor that is interfaced to Hamamatsu driver/amplifier and clock generator boards and a DRA laboratories 12-bit 160-kHz analog-to-digital converter. These are standard, commercially available devices which cost approximately $3500. The system is interfaced to and controlled by an IBM XT microcomputer. Detailed descriptions of the home-built detector housing and control/interface circuitry are presented and its application to the study of the reaction of horseradish peroxidase with hydrogen peroxide is demonstrated.

Elementary steps in the formation of horseradish peroxidase compound I: direct observation of compound 0, a new intermediate with a hyperporphyrin spectrum.

The reaction of horseradish peroxidase (HRP) with H2O2 has been studied in 50% v/v methanol/water over the 25.0 to -36.0 degrees C temperature range by using the low-temperature stopped-flow technique. All reactions were carried out under pseudo-first-order conditions with [H2O2] much greater than [HRP]. Arrhenius plots for the pseudo-first-order rate constant kobs were linear over the 17.6 to -36.0 degrees C temperature range studied with an activation energy of 4.8 +/- 0.5 kcal/mol. Above 0 degrees C, kobs varies linearly with peroxide concentration. However, saturation kinetics are observed below -16.0 degrees C, indicating that there is at least one reversible elementary step in this reaction. Double-reciprocal plots at -26.0 degrees C at pH* 7.3 for the reaction give kappa max(obs) = 163 s-1 and KM = 0.190 mM. Rapid-scan optical studies carried out at -35.0 degrees C with [H2O2] much greater than KM reveal the presence of a transient intermediate referred to as compound 0 whose conversion to compound I is rate limiting. The Soret region of the optical spectrum of compound 0 resembles that of a "hyperporphyrin" with prominent bands near 330 and 410 nm. The temperature dependencies of kappa max(obs) and KM have been measured over the -16.0 to -26.0 degrees C range and give an activation energy for kappa max(obs) of 1.6 +/- 0.7 kcal/mol and an enthalpy of formation for compound 0 of 4.0 +/- 0.7 kcal/mol.