Biomedical subjects

A Hassell

Publications and source records attributed to A Hassell.

3 recordsLinked to original sources

PubMed1992

Proteolysis of an active site peptide of lactate dehydrogenase by human immunodeficiency virus type 1 protease.

The muscle and heart lactate dehydrogenase (LDHs) of rabbit and pig are specifically cleaved at a single position by HIV-1 protease, resulting in the conversion of 36-kDa subunits of the oligomeric enzymes into 21- and 15-kDa protein bands as analyzed by SDS-PAGE. While the proteolysis was observed at neutral pH, it became more pronounced at pH 6.0 and 5.0. The time courses of the cleavage of the 36-kDa subunits were commensurate with the time-dependent loss of both quaternary structure and enzymatic activity. These results demonstrated that deoligomerization of rabbit muscle LDH at acidic pH rendered its subunits more susceptible to proteolysis, suggesting that a partially denatured form of the enzyme was the actual substrate. Proteolytic cleavage of the rabbit muscle enzyme occurred at a decapeptide sequence, His-Gly-Trp-Ile-Leu*Gly-Glu-His-Gly-Asp (scissile bond denoted throughout by an asterisk), which constitutes a "strand-loop" element in the muscle and heart LDH structures and contains the active site histidyl residue His-193. The kinetic parameters Km, Vmax/KmEt, and Vmax/Et for rabbit muscle LDH and the synthetic decapeptide Ac-His-Gly-Trp-Ile-Leu*Gly-Glu-His-Gly-Asp-NH2 were nearly identical, suggesting that the decapeptide within the protein substrate is conformationally mobile, as would be expected for the peptide substrate in solution. Insertion of part of this decapeptide sequence into bacterial galactokinase likewise rendered this protein susceptible to proteolysis by HIV-1 protease, and site-directed mutagenesis of this peptide in galactokinase revealed that the Glu residue at the P2' was important to binding to HIV-1 protease. Crystallographic analysis of HIV-1 protease complexed with a tight-binding peptide analogue inhibitor derived from this decapeptide sequence revealed that the "strand-loop" structure of the protein substrate must adopt a beta-sheet structure upon binding to the protease. The Glu residue in the P2' position of the inhibitor likely forms hydrogen-bonding interactions with both the alpha-amide and gamma-carboxylic groups of Asp-30 in the substrate binding site.

Amino Acid Sequence↗

PubMed1991

Peripheral nerve dysfunction in scleroderma.

Peripheral neuropathy in patients with scleroderma is thought to be rare. We have undertaken a quantitative assessment of peripheral nerve function in 29 patients with either limited cutaneous scleroderma or progressive systemic sclerosis. Tactile thresholds were raised in the fingers in 28 per cent of patients and in the foot in 50 per cent. Two-point discrimination was abnormal in 10 patients, thermal thresholds were abnormal in five and vibration thresholds were abnormal in one. Nerve conduction studies showed abnormalities in six patients, five of whom had clinical signs of a mild peripheral neuropathy: the mean duration of disease in these six patients was 10 years longer than that in the remainder of the patients. There was electrophysiological evidence of a subclinical carpal tunnel syndrome in two patients. The sympathetic skin response was recorded in 16 patients who had not been subjected to sympathectomy for Raynaud's phenomenon, and was abnormal in four. These results indicate that peripheral nerve dysfunction in scleroderma, though mild, is not as uncommon as previously thought. The abnormal cutaneous sensory thresholds may be partly due to altered viscoelastic properties of the skin, but abnormal responses in the lower limbs to tests of tactile sensitivity, the clinical findings and the disturbances of nerve conduction argue in favour of an additional neuropathic process in some patients. Low grade distal nerve trunk ischaemia may be responsible.

Adult↗

PubMed1991

Increased circulating levels of bromocriptine after vaginal compared with oral administration.

OBJECTIVE: To compare the circulating levels of bromocriptine after oral and vaginal administration of the drug. DESIGN: Experimental PARTICIPANTS: Seven ovulatory female volunteers and one hyperprolactinemic patient. INTERVENTIONS: Ovulatory volunteers were randomized to receive either oral or vaginal bromocriptine (2.5 mg). In a second session, the subjects were crossed-over to bromocriptine by the alternate route. An additional hyperprolactinemic patient received vaginal bromocriptine only. MAIN OUTCOME MEASURE: Serum bromocriptine and prolactin (PRL) levels were measured hourly for 12 hours in the normal volunteers and for 10 hours in the hyperprolactinemic patient. RESULTS: Circulating bromocriptine levels were significantly higher after vaginal bromocriptine after the 7th hour (P less than 0.05). The reduction in serum PRL was significantly greater after oral administration between 2 and 6 hours. CONCLUSIONS: Vaginally administered bromocriptine may result in a reduction in the overall dose required, thereby improving compliance without compromising therapeutic efficacy.

Administration, Oral↗