Cloning and expression in Escherichia coli of mature E1 beta subunit of bovine mitochondrial branched-chain alpha-keto acid dehydrogenase complex. Mapping of the E1 beta-binding region on E2.

A cDNA encoding the mature E1 beta subunit of the bovine branched-chain alpha-keto acid dehydrogenase complex was isolated from a lambda ZAP expression library. The bovine E1 beta cDNA is 1,393 base pairs in length. It encodes the entire mature E1 beta subunit consisting of 342 amino acid residues and a partial mitochondrial targeting presequence of 26 residues. The calculated molecular mass of the mature bovine E1 beta subunit is 37,776 daltons, and the calculated isoelectric point is pI 5.04. The mature bovine E1 beta subunit was expressed in Escherichia coli via the pKK233-2 vector in the presence of isopropyl beta-D-thiogalactopyranoside (IPTG). When expression was induced by IPTG at 37 degrees C, the soluble recombinant E1 beta subunit existed as a single high molecular weight form (Mr congruent to 3.5 x 10(5)), which sedimented during sucrose gradient ultracentrifugation at 2 x 10(5) x g. However, lowering the induction temperature to 25 degrees C resulted in the occurrence of both high and low molecular weight forms of the recombinant E1 beta protein. The low molecular weight form (Mr congruent to 9.1 x 10(4)) remained soluble after sucrose gradient centrifugation and was utilized in binding studies with a series of truncated recombinant E2 proteins. The results showed that the E1 beta subunit bound to the region between Ala-115 and Lys-150 of the E2 chain, which lay within the putative E3-binding domain. In contrast, the recombinant E1 alpha subunit did not bind the E2 component. The data suggest an apparent binding order of E2-E1 beta-E1 alpha, which supports and extends the model of E2 inner core deduced previously from the data of scanning transmission electron microscopy (Hackert, M.L., Xu, W.-X., Oliver, R.M., Wall, J.S., Hainfeld, J.F., Mullinax, T.R., and Reed, L.J. (1989) Biochemistry 28, 6816-6821). The relatively inaccessible topology of E1 beta may explain the lack of antigenicity and resistance to limited proteolysis of this subunit as it exists in the complex.     

Differential Effects of Chloral Hydrate and Pentobarbital Sodium on a Cocaine Level and Its Catecholamine Response in the Medial Prefrontal Cortex: A Comparison with Conscious Rats

Abstract: Adult male Sprague-Dawley rats anesthetized with chloral hydrate and pentobarbital sodium were used as two different treatment groups. Conscious rats were used as a control group. By using baseline (precocaine) concentration as 100%, after cocaine administration (3.0 mg/kg i.v.), the maximal dopamine (DA) increase occurring at the first microdialysis collection period (20 min) in the medial prefrontal cortex was 299 ± 46% for the chloral hydrate group, 168 ± 12% for the pentobarbital sodium group, and 325 ± 23% for the conscious group. At the same time, norepinephrine (NA) increases reached a maximum and were 162 ± 20%, 100 ± 5%, and 141 ± 17%, respectively. The maximal changes of DA and NA in the chloral hydrate group and in the control group were both significantly higher than that in the pentobarbital sodium group. Meanwhile, the cocaine concentration was higher over a 100-min period of time in the chloral hydrate group when compared with the pentobarbital group and the control group. The peak cocaine concentration in dialysate occurred in the same time slot of maximal DA and NA responses, which were 0.65 ± 0.08, 0.30 ± 0.02, and 0.41 ± 0.05 µ M , respectively. Anesthetics suppress the pharmacologic response of neurons, which may explain the difference in catecholamine response between the pentobarbital sodium and the conscious groups. Conversely, because there was no significant difference in DA and NA response between the chloral hydrate group and the conscious group, it may possibly be due to the balancing effect between the higher existing cocaine concentration and the anesthetic suppression on pharmacological response of neurons in the chloral hydrate group. The effect of guide cannula implantation on the cocaine-induced catecholamine response was also evaluated.     

The Rhodospirillum rubrum cytochrome bc1 complex: peptide composition, prosthetic group content and quinone binding

A cytochrome bc1 complex, essentially free of bacteriochlorophyll, has been purified from the photosynthetic purple non-sulfur bacterium Rhodospirillum rubrum. The complex catalyzes electron flow from quinol to cytochrome c (turnover number = 75 s-1) that is inhibited by low concentrations of antimycin A and myxothiazol. The complex contains only three peptide subunits: cytochrome b (Mr = 35,000); cytochrome c1 (Mr = 31,000) and the Rieske iron-sulfur protein (Mr = 22,400). Em values (pH 7.4) were measured for cytochrome c1 (+320 mV) and the two hemes of cytochrome b (-33 and -90 mV). Electron flow from quinol to cytochrome c is inhibited when the complex is pre-illuminated in the presence of a ubiquinone photoaffinity analog (azido-Q). During illumination, the azido-Q becomes covalently attached to the cytochrome b peptide and, to a lesser extent, to cytochrome c1.     

Effects of Obesity,Glucocorticoid, and Oral Contraceptive Therapy on Plasma Glucose and Blood Pyruvate Levels

The plasma glucose and blood pyruvate levels were determined after oral glucose tolerance test in six groups of women: non-obese and obese controls and in non-obese and obese women receiving glucocorticoid or oral contraceptive therapy. The mean fasting plasma glucose level was similar in all groups, but glucose tolerance was impaired in the obese controls, non-obese women on oral contraceptives or being treated with glucocorticoids, and appreciably impaired in the obese oral contraceptive and glucocorticoid groups compared with mean levels in non-obese subjects of the same groups. Obesity was associated with abnormally raised blood pyruvate levels in response to a glucose tolerance test in all groups. Striking similarities were observed between the responses of the plasma glucose and blood pyruvate levels to glucose tolerance tests in the obese control and non-obese oral contraceptive and non-obese glucocorticoid-treated groups. It is suggested that these abnormalities result from a common mechanism—namely, glucocorticoid excess.