Preferential cleavage at aspartyl-prolyl peptide bonds in dilute acid.

A simple, rapid technique is presented for preferential cleavage at aspartylprolyl peptide bonds. The method is based upon the fact that these peptide bonds are 8-20-fold more labile in 0.015 N HCl at 100-110 degrees than other aspartyl-X or X-aspartyl peptide bonds.

Pharmacokinetic interactions between digoxin and other drugs.

Drug interactions with digoxin are important because of this agent's narrow therapeutic index. Among the drugs that can decrease digoxin bioavailability are cholestyramine, antacid gels, kaolin-pectate, certain antimicrobial drugs and cancer chemotherapeutic agents. In selected patients, antibiotics may enhance digoxin bioavailability by eliminating intestinal flora that metabolize digoxin.

Assessment of the potential pharmacokinetic interaction between digoxin and ethmozine.

The potential for a pharmacokinetic interaction between the investigational antiarrhythmic drug ethmozine (moricizine HCl, the generic name that is infrequently used in existing literature) and digoxin was evaluated in nine healthy male adults. Serum and urinary digoxin concentrations were measured by radioimmunoassay following intravenous digoxin administration before and during steady-state ethmozine dosing. Plasma ethmozine levels following a single oral dose were measured before and after a single intravenous dose of digoxin.

Bioavailability of the bis- and monodigitoxosides of digitoxigenin.

The pharmacokinetic behavior of digitoxigenin is affected by the number of glycosides present. This study was conducted to compare the bioavailabilities of the bis- and monodigitoxosides of digitoxigenin in man. Intravenous and oral doses of the two drugs were administered to six normal volunteers.

Distribution of a COOH-terminal amino acid extension of liver fructose-1,6-bisphosphatase among rodent species.

We have recently established from sequence analysis that rat liver fructose-1,6-bisphosphatase contains a 24-26 residue extension beyond the COOH-terminal amino acid of other mammalian fructose-1,6-bisphosphatases that results in an increased subunit molecular weight (Rittenhouse et al. (1983) J. Biol.

Comparison of a QRS scoring system for estimating acute infarct size with radionuclide left ventriculography.

A QRS scoring system was compared with left ventricular ejection fraction (LVEF) in 40 patients enrolled in the Multicenter Post Infarction Program. A poor correlation was found between these two parameters. Possible reasons for these findings include the fact that the radionuclide studies were performed at several institutions or that there was a mean interval of 6 days between the time of the ECG and the radionuclide studies.

Kinetics of digitoxin and the bis- and monodigitoxosides of digitoxigenin in renal insufficiency.

The kinetics of digitoxin and two of its major metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six subjects with renal insufficiency and compared to those in six age- and sex-matched normal control subjects. No significant differences between the two groups were found in elimination t 1/2, total body clearance, or volume of distribution. Average renal clearances of all three drugs were reduced in subjects with renal failure, but the differences were significant only in the case of digitoxin.

Kinetics of digitoxin and the bis- and monodigitoxosides of digitoxigenin in normal subjects.

The kinetics of digitoxin and two of its metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six normal subjects. Mean t 1/2s and total body clearances were 134.4, 15.

Prognosis of patients with diabetes mellitus after acute myocardial infarction.

Sixty patients with diabetes mellitus who survived the coronary care unit phase of acute myocardial infarction (AMI) were followed an average of 19 months and the prognosis of diabetic patients was compared with that of 719 nondiabetic patients. The mortality rate was 25% in diabetic patients and 8% in nondiabetic patients. These patients had been entered in a Multicenter Postinfarction Program, where analysis of the total data base showed 4 significant prognostic factors: cardiac symptoms before AMI, pulmonary rales when the patient was in the coronary care unit, more than 10 ventricular premature complexes per hour recorded on Holter monitor just before discharge, and a radionuclide ejection fraction of less than 40%.

Preliminary X-ray crystallographic studies of pig kidney fructose-1,6-bisphosphatase.

Preliminary x-ray data have been obtained from large single crystals of pig kidney fructose-1,6-bisphosphatase, grown from polyethylene glycol. The crystals have the symmetry of space group P3(1)21 or its enantiomorph P3(2)21, contain two subunits of the 146,000-dalton tetramer/asymmetric unit, and diffract to 2.9-A resolution on still photographs.

Peptide mapping by polyacrylamide gel electrophoresis after cleavage at aspartyl-prolyl peptide bonds in sodium dodecyl sulfate-containing buffers.

Protein samples prepared for sodium dodecyl sulfate-polyacrylamide gel electrophoresis are preferentially cleaved at aspartyl-prolyl peptide bonds upon heating at 110 degrees C. The presence of aspartyl-prolyl peptide bonds in a protein can therefore be detected by gel electrophoresis of heated samples and the resulting peptides mapped. The method of heat cleavage also works well with proteins in bands cut from electrophoresed gels using modified stacking conditions in the second electrophoresis.

A re-evaluation of the molecular weight of yeast (Saccharomyces cerevisiae) fructose-1,6-bisphosphatase.

In contrast with previous results that indicate that Saccharomyces cerevisiae fructose-1,6-bisphosphatase is a dimer of 56,000 molecular weight subunits, we find that the subunit Mr of the enzyme purified from baker's yeast is 40,000. The same subunit Mr was observed in immunoprecipitates of crude supernatants of baker's yeast and S. cerevisiae cultures, as well as in acid-extracts of cells detected by immunoblotting, suggesting that the native subunit indeed has a Mr of 40,000 and it has not been produced from a larger polypeptide.

Inhibition of Escherichia coli fructose-1,6-bisphosphatase by fructose 2,6-bisphosphate.

Fructose 2,6-bisphosphate, a potent inhibitor of fructose-1,6-bisphosphatases, was found to be an inhibitor of the Escherichia coli enzyme. The substrate saturation curves in the presence of inhibitor were sigmoidal and the inhibition was much stronger at low than at high substrate concentrations. At a substrate concentration of 20 microM, 50% inhibition was observed at 4.

Identification of the highly reactive sulfhydryl group of pig kidney fructose 1,6-bisphosphatase at cysteine 128.

Fructose 1,6-bisphosphatases contain a highly reactive cysteine residue, the reactivity of which is influenced by ligands that bind at the catalytic and at the allosteric AMP sites of the enzyme. Nevertheless, the sulfhydryl group appears to be proximal to these sites and not a functional component of either. Modification of pig kidney fructose 1,6-bisphosphatase with three reagents, 5,5'-dithiobis-(2-nitrobenzoic acid), iodoacetamide, and phenacyl bromide, yields derivatives with similar properties, thus suggesting that the same residue was modified in each case.

Identification of the in vivo and in vitro phosphorylation sites of rat liver fructose 1,6-bisphosphatase.

Rat liver fructose 1,6-bisphosphatase appears to be unique in that it extends 24-26 residues beyond the COOH-terminal amino acid of other mammalian fructose 1,6-bisphosphatases and this extension contains phosphorylation sites. Using as a frame of reference the 335-residue sequence of pig kidney fructose 1,6-bisphosphatase (Marcus, F., Edelstein, I.

Prognosis after myocardial infarction.

There is 10-20 percent mortality in the first two years after hospital discharge from a myocardial infarction. Patient management would be facilitated if one could stratify patients into those who have a low, medium or high risk of death within the first two years following infarction. Towards achieving this end a multicenter study was designed.

Pharmacokinetics and bioavailability of digitoxin by a specific assay.

The pharmacokinetics and bioavailability of digitoxin were examined in six normal human subjects using an assay that separates digitoxin from its metabolites. After intravenous administration, the mean systemic clearance was 2.44 ml/min; the volume of distribution was 0.

Quantitation of digitoxin and the bis- and monodigitoxosides of digitoxigenin in serum.

A specific assay is described for measuring the concentration of digitoxin and the bis- and monoglycosides of digitoxigenin in serum. The procedure includes: (1) addition of a tracer amount of tritium labeled parent compound to the serum in order to measure percentage recovery; (2) solvent extraction to separate polar and non-polar metabolites; (3) reversed-phase thin-layer chromatography of the non-polar fraction to separate digoxigenins from digitoxigenins; (4) thin-layer chromatography to isolate digitoxin, and the bis- and monoglycosides of digitoxigenin; and (5) use of an 125I-radioimmunoassay to determine the concentration of the glycosides. Each of these three glycosides was administered intravenously to a normal subject, and the concentration of parent compound was measured in the serum at various times.

Drug interactions with amiodarone.

There are a number of important drug interactions with amiodarone. This agent appears to have a marked effect on the kinetics of some commonly used cardiovascular drugs, such as warfarin, digoxin, quinidine, and procainamide, and has dynamic interactions with others, such as the beta blockers and some calcium antagonists. Bleeding has been reported, apparently caused by a potentiation of the anticoagulant effect of warfarin by amiodarone.