Biomedical subjects

M Wahab

Publications and source records attributed to M Wahab.

24 records · Page 2Linked to original sources

PubMed1997

Neural network analysis of Doppler ultrasound blood flow signals: a pilot study.

It has been hypothesised that each artery in the human body has its own characteristic "signature" -a unique Doppler flow profile which can identify the artery and which may also be modified by the presence of disease. To test this hypothesis an artificial neural network (ANN) was trained to recognise three groups of maximum frequency envelopes derived from Doppler ultrasound spectrograms; these were the common carotid, common femoral and popliteal arteries. Data were collected from 24 subjects known to have no significant atheromatous disease. The maximum frequency envelopes were used to create sets of training and testing vectors for a backpropagation ANN. The ANN demonstrated a high success rate for appropriate classification of the test vectors: 100% for the carotid; 92% for the femoral; and 96% for the popliteal artery. This work has demonstrated the ability of the ANN to differentiate accurately between different and similar flow profiles, outlining the potential of this technology to identify subtle changes induced by the onset of arterial disease within a specific vessel. It should be noted that the ANN not only models the maximum frequency envelope but also, unlike standard indices, makes a decision as to which artery the maximum frequency envelope belongs to, thus providing the potential to obviate human subjective classification.

Adult↗

PubMed1997

The effect of long-term oestradiol implantation on bone mineral density in postmenopausal women who have undergone hysterectomy and bilateral oophorectomy.

Twelve women who had received oestradiol implantation on demand for at least 15 years following hysterectomy with bilateral oophorectomy, underwent bone densitometry of hip and spine. Bone mass of hip and spine was significantly elevated above that of both the age matched mean to a degree hitherto undocumented. This suggests that oestrogen in high doses or over a long period may produce a true anabolic effect on bone mass.

Absorptiometry, Photon↗

PubMed1994

Classification of serine proteases derived from steric comparisons of their active sites, part II: "Ser, His, Asp arrangements in proteolytic and nonproteolytic proteins".

The assignment of serine proteases to the families of (chymo)trypsins and subtilisins, respectively, is extended by including additional data from the Brookhaven Protein Data Bank. To better understand basic properties connected with this type of assignment the steric situation in the vicinity of the tetrad aminoacyl residues and atomic distances within the tetrads are considered. A new catalytic mechanism is suggested based on differences between tonin and kallikrein with respect to structure and reactivity of the catalytic tetrad. All protein structures available from the Brookhaven Protein Data Bank are analyzed with regard to the occurrence of Asp....His....Ser triads.

Amino Acid Sequence↗

PubMed1993

Classification of serine proteases derived from steric comparisons of their active sites.

The steric arrangements of the amino acyl residues in the catalytic triads and tetrads of the active site are compared with each other by means of systematic analysis of the conformation of the serine proteases stored in the Brookhaven Protein Data Bank. On this basis a differentiation between the representatives of the (chymo)trypsin family on the one hand and those of the subtilisin family on the other hand is found. The enzyme tonin distinguishes from representatives of the (chymo)trypsin family and should be classified to a new subclass of this family. Thermitase represents a new subclass of the subtilisins. The spatial orientation of the amino acyl residues of the active site of tonin suggests a new mechanism of enzyme catalysis that possibly also occurs in dipeptidyl peptidase IV.

Binding Sites↗

PubMed1991

Conformational analysis of the tetrapeptide Pro-D-Phe-Pro-Gly in aqueous solution.

Conformational investigations of the tetrapeptide Pro-D-Phe-Pro-Gly in water solution were carried out by 1H and 13C NMR spectroscopy. The internal proline residue allows for the possibility of cis/trans isomerization about the D-Phe-Pro peptide bond resulting in two conformational isomers. The major isomer was identified as the trans isomer. The pH-dependence of the cis/trans equilibrium supports an additional stabilisation of the trans isomer by an intramolecular ionic interaction between the amino- and carboxy-terminus in the zwitterionic state. Based on 13C spin-lattice relaxation times (T1), different pyrrolidine ring conformations of Pro1 and Pro3 could be determined. By combination of several NMR data (vicinal coupling constants 3JN alpha, temperature dependence of the NH chemical shifts, differences in the chemical shifts between the beta and gamma carbons of the proline residues) and energy minimization calculations, a type II' beta-turn should contribute considerably to the overall structure of the trans isomer.

Endorphins↗

PubMed1991

HAMOG: molecular graphics program for chemistry, biochemistry, molecular biology and enzyme research.

HAMOG is a computer graphics program written in C for personal computers. Clear menus and a context-sensitive help option make the program easy to operate for occasional users. HAMOG provides a flexible environment for displaying and manipulating molecules and molecular systems. Special functions allow the investigation of structure-activity relationships of biologically active molecules. These include the calculation of molecular electrostatic potentials and fields, the superposition of molecules and the calculation of steric accessibilities. The visualization and manipulation of protein structures immediately readable from the Brookhaven Protein Data Bank files are also possible using HAMOG. The construction of any peptide or protein structure is very simple.

Chemical Phenomena↗