Search PubMed⌕ Search

Biomedical subjects

A Heitz

Publications and source records attributed to A Heitz.

At least 37 records · Page 2Linked to original sources
PubMed1995

Folding of the squash trypsin inhibitor EETI II. Evidence of native and non-native local structural preferences in a linear analogue.

A peptide, corresponding to the entire sequence of the squash trypsin inhibitor EETI II (Ecballium elaterium trypsin inhibitor) in which the six cysteines, engaged in three disulphide bridges in native EETI II, have been replaced by six serines, has been synthesised. CD, Fourier-transform infrared spectroscopy (FTIR) and 1H-NMR studies of this peptide revealed that some secondary structures present in native EETI II are still populated in the absence of disulphide bonds. Native-like secondary structures were observed for segments 10-15 (helix), 16-19 and 22-25 (reverse turns) but no native tertiary interaction was detected. However, a non-native local interaction between the aromatic ring of Phe26 and the amide group of Gly28 was observed. It is hypothesised that the 10-15, 16-19 and 22-25 native-like local conformations could play a major role in the early folding of EETI II.

Amino Acid Sequence↗
PubMed1994

Protein sparing on very low calorie diets: ground squirrels succeed where obese people fail.

During seasonal cycles in ground squirrels, as in many other species, there are periods of spontaneous loss of appetite, very low calorie intake and a 30% loss in body mass. Measurements of nitrogen balance during early and later stages of the mass loss phase of the cycle (-1.2 +/- 6.7 and +13.1 +/- 8.8 mg/24 h, respectively) showed a total sparing of protein, indicating a selective use of fat. However, when no food at all was available, nitrogen balance was negative (-45 +/- 5 mg/24 h). Provided that they have access to some food, ground squirrels are therefore able to compensate for any protein utilization, while at the same time selectively losing large amounts of fat. It appears that a factor related to spontaneous reduction in food intake enables these animals to achieve the total sparing of protein that eludes dieting humans on comparably low caloric intakes.

Animals↗
PubMed1993

Characterization and 2D NMR study of the stable [9-21, 15-27] 2 disulfide intermediate in the folding of the 3 disulfide trypsin inhibitor EETI II.

The three disulfide Ecballium elaterium trypsin inhibitor II (EETI II) reduction with dithiothreitol (DTT) and reoxidation of the fully reduced derivative have been examined. A common stable intermediate has been observed for both processes. Isolation and sequencing of carboxymethylated material showed that the intermediate lacks the [2-19] bridge. The NMR study showed a very strong structural conservation as compared to the native EETI II, suggesting that the bridges are the [9-21] and [15-27] native ones. The differences occurred in sections 2-7 (containing the free cysteine 2 and the Arg 4-Ile 5 active site) and 19-21 (containing the second free cysteine). Distance geometry calculations and restrained molecular dynamics refinements were also in favor of a [9-21, 15-27] arrangement and resulted in a well-conserved (7-28) segment.

Amino Acid Sequence↗
PubMed1993

Body protein and lipid deficit in tumour-bearing rats in relation to age.

Cancer cachexia is among the most dramatic situations of depletion in body energy reserves. To ascertain whether the pattern of body composition alteration during tumour development is influenced by aging as in uncomplicated starvation, we compared the difference of body composition between Yoshida sarcoma bearing rats and young (200 g, 7 weeks) and adult (400 g, 13 weeks) control rats. After the same duration of tumour bearing, mass and composition of tumours were similar in adult and young rats, indicating that they are independent of host age. Food intake decreased to a remarkably similar value in both young and adults. Body water content was elevated in hosts of both ages. The relative deficit of body lipid vs controls was similar for both, the absolute lipid deficit being therefore larger in adult than in young tumour-bearing rats (14.3 +/- 4.4 g vs 6.8 +/- 0.9 g; P < 0.01). In contrast, there was a relatively larger deficit of body protein in young rats. Paradoxically, these rats still maintained a positive nitrogen balance whereas this balance was negative in adult tumour-bearing rats. In conclusion, as previously shown in uncomplicated undernutrition, the anorexia induced by Yoshida sarcoma development is still associated with some protein accretion in young rats whereas cachexia develops in adults.

Aging↗
PubMed1993

Solution conformation of a synthetic bis-headed inhibitor of trypsin and carboxypeptidase A: new structural alignment between the squash inhibitors and the potato carboxypeptidase inhibitor.

The trypsin carboxypeptidase peptide inhibitor (TCPI) which inhibits both trypsin and carboxypeptidase A has been chemically engineered by modification of the Ecballium elaterium trypsin inhibitor II (EETI-II). The solution conformation of TCPI, studied by two-dimensional nuclear magnetic resonance, was shown to be very close to those of squash inhibitors. Only limited deviations of the trypsin binding loop compared to its location in the EETI-II/trypsin complex were detected. It was also shown that the position of the C-terminal tail did not significantly change from the position observed in the complex between carboxypeptidase A and the potato carboxypeptidase inhibitor (PCI). The conformation of TCPI was carefully compared with the PCI one and a new structural alignment between the two microproteins is proposed. This alignment points out the very good conservation in the two inhibitors of a subdomain comprising segments 7-15, 19-22 and 25-28. Most importantly, the 2-19 disulfide bridge of TCPI was not structurally conserved in PCI and appeared to be rather unimportant for the early folding process of these molecules. This result agrees with the recent observation that the 2-19 bridge is the last to be formed in the folding of the squash inhibitor EETI-II and suggests that this is also the case during the folding of the potato carboxypeptidase inhibitor.

Amino Acid Sequence↗
PubMed1993

Heat stress does not modify lactate exchange and removal abilities during recovery from short exercise.

Arterial and femoral venous lactate concentrations were measured before, during, and after short intermittent exercise (55-118% of maximal O2 consumption) in thermoneutral (N, 25 degrees C, 10.5 Torr) and hot (H, 45 degrees C, 17.5 Torr) conditions. The thermal load induced significantly higher heart rate and rectal temperature in H relative to N. All the arterial lactate (La) recovery curves were fitted to an equation containing two exponential time functions of the form La(t) = La(0) + A1a(1 - e-gamma 1at) + A2a(1 - e-gamma 2at) where the velocity constants gamma 1a and gamma 2a are the body's overall ability to exchange and remove lactate after exercise, respectively, and t is time. There was no significant difference in these constants, regardless of thermal conditions. The arterial lactate concentration at the end of exercise, the peak lactate concentration during recovery, the amplitudes A1a and A2a of the biexponential function, and the arteriofemoral venous lactate concentration difference during recovery were not significantly different in H relative to N. However, measured and computed arterial lactate concentrations during recovery, especially at the end of the tests, were higher in H (P < 0.04). The more elevated lactate concentrations in H at rest at the end of recovery denote a higher basal lactate production, and they were not due to muscle hypoxia.

Adult↗
PubMed1992

Relationships between lipid availability and protein utilization during prolonged fasting.

Mammals and birds adapt to prolonged fasting by mobilizing fat stores and minimizing protein loss. This strategy ends with an increase in protein utilization associated with behavioural changes promoting food foraging. Using the Zucker rat as a model, we have investigated the effect of severe obesity on this pattern of protein loss during long-term fasting. Two interactions between the initial adiposity and protein utilization were found. First, protein conservation was more effective in obese than in lean rats: fatty rats had a three times lower daily nitrogen excretion and proportion of energy expenditure deriving from proteins, and a lower daily protein loss in various muscles. This phase of protein sparing is moreover nine times longer in the fatty rats. Second, obese animals did not show the late increase in nitrogen excretion that occurred in their lean littermates. Total body protein loss during starvation was larger in fatty rats (57% versus 29%) and, accordingly, total protein loss was greater in their muscles. At the end of the experiment, lean and obese rats had lost 98% and 82%, respectively, of their initial lipid reserves, and fatty rats still had an obese body composition. These results support the hypothesis that in severely obese humans and animals a lethal cumulative protein loss is reached long before the exhaustion of fat stores, while the phase of protein conservation is still continuing. In contrast, in lean rats, survival of fasting seems to depend on the availability of lipid fuels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1992

Caffeic glycoside esters from Jasminum nudiflorum and some related species.

Poliumoside, forsythoside B, echinacoside and arenarioside, caffeic glycoside esters, were isolated from several species of Oleaceae. The poliumoside/forsythoside ratio distinguishes Jasminum nudiflorum from J. mesnyi. Arenarioside and forsythoside B act in Forsythia species as good hybridization markers.

Caffeic Acids↗
PubMed1990

Blood lactate during constant-load exercise at aerobic and anaerobic thresholds.

Venous blood lactate concentrations [1ab] were measured every 30 s in five athletes performing prolonged exercise at three constant intensities: the aerobic threshold (Thaer), the anaerobic threshold (Than) and at a work rate (IWR) intermediate between Thaer and Than. Measurements of oxygen consumption (VO2) and heart rate (HR) were made every min. Most of the subjects maintained constant intensity exercise for 45 min at Thaer and IWR, but at Than none could exercise for more than 30 min. Relationships between variations in [1ab] and concomitant changes in VO2 or HR were not statistically significant. Depending on the exercise intensity (Thaer, IWR, or Than) several different patterns of change in [1ab] have been identified. Subjects did not necessarily show the same pattern at comparable exercise intensities. Averaging [1ab] as a function of relative exercise intensity masked spatial and temporal characteristics of individual curves so that a common pattern could not be discerned at any of the three exercise levels studied. The differences among the subjects are better described on individual [1ab] curves when sampling has been made at time intervals sufficiently small to resolve individual characteristics.

Aerobiosis↗
PubMed1990

Comparative lactate kinetics after short and prolonged submaximal exercise.

Arterial blood lactate concentrations were determined in two groups of eleven males before, during and after near 2 W.kg body mass-1 bicycle exercise. One group of subjects cycled for 3 min, whereas the second group exercised for 60 min. All the lactate curves during recovery could be fitted to a bi-exponential time function consisting of a rapidly increasing and a slowly decreasing component. This typical evolution pattern indicates that the two-compartment model which has been proposed to represent the movements of lactate after short exercise applies also to recovery from prolonged exercise. Lengthening exercise duration decreased (respectively 10% and 28%) the value of both velocity constants of the fits to the lactate recovery curves, with the difference (28%) being statistically significant for the velocity constant describing the slowly decreasing part of the curves. This result indicates that extending exercise from 3 to 60 min impairs the ability to remove lactate after the exercise.

Adult↗
PubMed1990

Lactate removal ability and graded exercise in humans.

Venous lactate concentrations of nine athletes were recorded every 5 s before, during, and after graded exercise beginning at a work rate of 0 W with an increase of 50 W every 4th min. The continuous model proposed by Hughson et al. (J. Appl. Physiol. 62: 1975-1981, 1987) was well fitted with the individual blood lactate concentration vs. work rate curves obtained during exercise. Time courses of lactate concentrations during recovery were accurately described by a sum of two exponential functions. Significant direct linear relationships were found between the velocity constant (gamma 2 nu) of the slowly decreasing exponential term of the recovery curves and the times into the exercise when a lactate concentration of 2.5 mmol/l was reached. There was a significant inverse correlation between gamma 2 nu and the rate of lactate increase during the last step of the exercise. In terms of the functional meaning given to gamma 2 nu, these relationships indicate that the shift to higher work rates of the increase of the blood lactate concentration during graded exercise in fit or trained athletes, when compared with less fit or untrained ones, is associated with a higher ability to remove lactate during the recovery. The results suggest that the lactate removal ability plays an important role in the evolution pattern of blood lactate concentrations during graded exercise.

Adolescent↗
PubMed1990

[Evaluation of the cost-efficacy ratio of Pall BB 22 15 filters for the bacterial protection of anesthesia circuits].

The aim of this study is to assess wether the use of the bacteriological filter Pall BB 22 15 placed on the Y piece of the anesthesia equipment decreases contamination and furthermore to evaluate the cost of this practice versus changing anesthetic circuits after every patient. Randomized trials are conducted with three "Engström" machines in three cardiac surgery operating rooms. The Y pieces were examined with qualitative and quantitative bacteriological analysis. Use filters is less expensive than changing circuit for each patient for a comparable efficacy.

Air Microbiology↗
PubMed1989

1H 2D NMR and distance geometry study of the folding of Ecballium elaterium trypsin inhibitor, a member of the squash inhibitors family.

The solution conformation of synthetic Ecballium elaterium trypsin inhibitor II, a 28-residue peptide with 3 disulfide bridges, has been studied by 1H 2D NMR measurements. Secondary structure elements were determined: a miniantiparallel beta-sheet Met 7-Cys 9 and Gly 25-Cys 27, a beta-hairpin 20-28 with beta-turn 22-25, and two tight turns Asp 12-Cys 15 and Leu 16-Cys 19. A set of interproton distance restraints deduced from two-dimensional nuclear Overhauser enhancement spectra and 13 phi backbone torsion angles restraints were used as the basis of three-dimensional structure computations including disulfide bridges arrangement by using distance geometry calculations. Computations for the 15 possible S-S linkage combinations lead to the proposal of the array 2-19, 9-21, 15-27 as the most probable structure for EETI II.

Amino Acid Sequence↗
PubMed1989

Use of restrained molecular dynamics in water to determine three-dimensional protein structure: prediction of the three-dimensional structure of Ecballium elaterium trypsin inhibitor II.

Refinement of distance geometry (DG) structures of EETI-II (Heitz et al.: Biochemistry 28:2392-2398, 1989), a member of the squash family trypsin inhibitor, have been carried out by restrained molecular dynamics (RMD) in water. The resulting models show better side chain apolar/polar surface ratio and estimated solvation free energy than structures refined "in vacuo." The consistent lower values of residual NMR constraint violations, apolar/polar surface ratio, and solvation free energy for one of these refined structures allowed prediction of the 3D folding and disulfide connectivity of EETI-II. Except for the few first residues for which no NMR constraints were available, this computer model fully agreed with X-ray structures of CMTI-I (Bode et al.: FEBS Lett. 242:285-292, 1989) and EETI-II complexed with trypsin that appeared after the RMD simulation was completed. Restrained molecular dynamics in water is thus proved to be highly valuable for refinement of DG structures. Also, the successful use of apolar/polar surface ratio and of solvation free energy reinforce the analysis of Novotny et al. (Proteins 4:19-30, 1988) and shows that these criteria are useful indicators of correct versus misfolded models.

Amino Acid Sequence↗
PubMed1989

Effect of exercise duration on lactate kinetics after short muscular exercise.

Arterial blood lactate concentrations were measured in six normal males before, during and after 3- and 6-min bicycle exercises performed at three different work rates. The lactate recovery curves were fitted to a bi-exponential time function consisting of a rapidly increasing and a slowly decreasing component, which supplied an accurate representation of the changes in lactate concentration. Variations in the parameters of this mathematical model have been studied as a function of the duration of exercise and of the work rate, showing a clear dependence on exercise duration such that increasing exercise length decreases the velocity constants of the fitted curves. In terms of the functional meaning which can be given to these constants, this result indicates that extending exercise duration from 3 to 6 min reduces the ability of the whole body to exchange and remove lactate. This effect did not qualitatively modify the one already described, which is due to increased work rates, but it shifted the ability to exchange and remove lactate towards lower values. The main conclusion of the study is that lactate kinetic data vary as a function of time during exercise. This inference must be accounted for in the interpretation of lactate data obtained during muscular exercise.

Adult↗
PubMed1989

Comparison of arterial and venous blood lactate kinetics after short exercise.

Seventeen healthy male volunteers participated in this study designed to compare arterial with both arterialized venous and venous lactate kinetics after short exercise. Blood samples drawn before, during, and after bicycle exercise were analyzed continuously for lactate. A mathematical function incorporating two exponential terms was fitted to the arterial, arterialized venous, and venous lactate recovery curves, and the parameters of the mathematical function were compared using a linear regression. All parameters measured on or fitted to the arterialized venous curves correlated well with the respective arterial data (correlation coefficient R = 0.82 to 0.99, P less than 0.001). Among the parameters obtained from the fit to the venous curves, only those describing lactate removal correlated closely with the arterial results. It is concluded that for lactate kinetic studies during recovery following short-term muscular exercise, the information obtained from arterialized venous blood is comparable to arterial blood, whereas the use of venous blood, from the sampling site in this study, appears suitable for determining only the parameters for lactate disappearance. These conclusions are illustrated by the comparison between arterial, arterialized venous, and venous parameters as a function of the work rate of the previously performed exercise.

Adult↗