Reengineering the catalytic lysine of aspartate aminotransferase by chemical elaboration of a genetically introduced cysteine

The active-site essential catalytic residue of aspartate aminotransferase, Lys 258, has been converted to Cys (K258C) by site-directed mutagenesis. This mutant retains less than 10(-6) of the wild-type activity with L-aspartate. The deleted general base was functionally replaced by selective (with respect to the other five cysteines in wild type) aminoethylation of the introduced Cys 258 with (2-bromoethyl)amine following reversible protection of the nontarget sulfhydryl groups at different stages of unfolding. The chemically elaborated mutant (K258C-EA) is 10(5) times more reactive than is K258C and has a kcat value of approximately 7% of that of wild type (WT). Km and KI values are similar to those for WT. The acidic pKa controlling V/KAsp is shifted from 7.3 (WT) to 6.0 (mutant). V/K values for amino acids are approximately 3% of those found for WT, whereas they are approximately 20% for keto acids. The value of DV increases from 1.6 for WT to 3.4 for the mutant, indicating that C alpha proton abstraction constitutes a more significant kinetic barrier for the latter enzyme. A smaller, but still significant, increase in D(V/KAsp) from 1.9 in WT to 3.0 in the mutant shows that the forward and reverse commitment factors are inverted by the mutation. The acidic limb of the V/KAsp versus pH profile, is lowered by 1.3 pH units, probably reflecting the similar difference in the basicity of the epsilon-NH2 group in gamma-thialysine versus that in lysine.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequential protection-modification method for selective sulfhydryl group derivatization in proteins having more than one cysteine

The method of Smith and Hartman [J. Biol. Chem., 263, 4921-4925 (1988)] for introducing the non-natural lysine analog, S-(2-aminoethyl)cysteine, into specific sites in proteins by alkylation of a genetically introduced cysteine with 2-bromoethylamine has been generalized to be applicable to proteins containing one or more endogenous cysteines. The target cysteine residue introduced at the active site of aspartate aminotransferase is protected by bound cofactor. The enzyme is partially unfolded in low concentrations of urea, and the non-active site cysteine residues derivatized by a reversible thiol protecting reagent. The active site cysteine is then exposed and alkylated in 6 M urea. Enzyme activity is regenerated by removal of the thiol protecting groups and refolding of the protein.

[Peroperative management of the orthotopic implant of a Jarvik-7 total cardiac prosthesis]

A 31 years old woman with a terminal phase dilated cardiomyopathy and a ventricular ejection fraction of 0.12 was admitted to our hospital to be included in the cardiac transplantation program. When entering the hospital her condition worsened and she suffered an electromechanical dissociation that needed cardiopulmonary resuscitation. Few hours later, energetic medical treatment could not improve her haemodynamic situation. Having no adequate organ available for emergency transplantation, a total orthotopic prosthesis (Jarvik-7-70) implantation was decided. Anesthesia was maintained with fentanyl (50 micrograms/kg), droperidol (0.23 mg/kg) and diazepam (0.25 mg/kg). There were no incidents during or after extracorporeal circulation bypass; despite the use of furosemide (100 mg) and mannitol (1 g/kg) diuresis was less than 40 ml/h. After by-pass, pulmonary hypertension was observed and treated with sodium nitroprusside (1 microgram/kg/min) and isoproterenol (5 micrograms/kg/min), as well as increasing the right ventricle working pressure of the device from 40 to 70 mmHg, obtaining haemodynamic stabilization and good tissular perfusion. After operation, the patient arrived to the Recovery Unit in a steady situation, with a cardiac index of 2.87 l/min/m2 and a diuresis of 150 ml/h. Some other aspects of the anaesthetic management are also discussed in this paper.

[Anesthesia in heart transplantation. Experience at the Clínica Puerto de Hierro]

The anaesthetic management of 41 patients who underwent cardiac transplantation during a 40 month period at Clínica Puerta de Hierro is reviewed. The study includes the preoperative assessment, anaesthetic agents used and intraoperative incidences. The anaesthesia was induced with etomidate whereas a high-dose fentanyl, supplemented with diazepam, was the most commonly anaesthetic technique used. There was no intraoperative mortality in this series. Several interesting concerns related to the physiology of the denervated heart and the effects of vasoactive agents after extracorporeal circulation are reviewed.

Cardiovascular and respiratory complications after elective supratentorial craniotomy

The cardiovascular and respiratory complications and their treatment during the immediate postoperative period in the intensive care unit (ICU) are analyzed in 145 consecutive cases of supratentorial craniotomy. In this series, 87.5% of the patients remained in the unit less than 48 hours. In all, 67 cardiovascular disorders were observed in 49 subjects (33.7%). Supraventricular tachycardia, arterial hypotension and hypertension were, in order of frequency, the most common hemodynamic alterations. Fifty percent of the arterial hypertensions were treated with vasodilators. The etiological cause of hypotension was hypovolemia in 66.6% of the cases. Extubation was not performed in the operating room in 17.93% of the subjects, and seven patients in which it was had to be reintubated. The stay in the ICU was longer for those intubated (3.03 +/- 0.77 days). Mortality was 2.06%.

Efficient transformation of previously activated and dividing T lymphocytes by human T cell leukemia-lymphoma virus

Modifying previously reported techniques, we attempted to increase the efficiency of human T cell leukemia-lymphoma virus (HTLV) transformation of human T lymphocytes. Lethally irradiated donor cells (DCs) were cultured with target mononuclear cells (TMCs). DCs included ten HTLV+ T cell lines with varying degrees of virus expression or seven cell lines that do not express HTLV. TMCs were prepared from 20 cord and 16 adult peripheral blood samples, including eight patients with acquired immunodeficiency syndrome (AIDS). TMCs were either added directly to the DCs or were first stimulated with phytohemagglutinin (PHA) (5 micrograms/mL) and grown in T cell growth factor (TCGF) prior to exposure to DCs. The presence of integrated HTLV proviral DNA in the transformed cells was determined by dot blot hybridization, utilizing a cloned probe to the HTLV-I genome. HTLV production by transformed TMCs was assessed for HTLV p19, reverse transcriptase, and virus particles. No transformation occurred with T cell donor lines that do not express HTLV. Low virus expressor DCs could only, with rare exception, transform preactivated TMCs. High-titer virus-producing DCs could transform activated and nonactivated cord blood cells and activated adult TMCs. Only MT-2 could routinely transform nonactivated normal adult and activated AIDS TMCs. HUT 102 B2 could transform only one activated AIDS sample, the cells of which initially expressed HTLV-like proteins and virions. Transformed cell lines contained subsets of mature T lymphocytes with variable HTLV expression. Prior activation and culture of the T lymphocytes increases the probability and rate of transformation by HTLV, allowing for biologic detection of low HTLV-producing cells and for in vitro expansion of T lymphocyte subsets from selected patients.