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Biomedical subjects

H Venter

Publications and source records attributed to H Venter.

8 recordsLinked to original sources
PubMed2005

Similarities between ATP-dependent and ion-coupled multidrug transporters.

The movement of drugs across biological membranes is mediated by two major classes of membrane transporters. Primary-active, ABC (ATP-binding cassette) multidrug transporters are dependent on ATP-binding/hydrolysis, whereas secondary-active multidrug transporters are coupled to the proton (or sodium)-motive force that exists across the plasma membrane. Recent work on LmrA, an ABC multidrug transporter in Lactococcus lactis, suggests that primary- and secondary-active multidrug transporters share functional and structural features. Some of these similarities and their implications for the mechanism of transport by ABC multidrug transporters will be discussed.

Adenosine Triphosphate↗
PubMed1999

Purification and characterization of a metalloprotease from Chryseobacterium indologenes Ix9a and determination of the amino acid specificity with electrospray mass spectrometry.

The heat-stable protease from Chryseobacterium indologenes Ix9a was purified to homogeneity using immobilized metal affinity chromatography. The enzyme was characterized as a metalloprotease with an approximate relative molecular mass of 24,000, a pH optimum of 6.5, and a high temperature optimum (50 degrees C). The metal chelator EDTA and the Zn2+-specific chelator 1,10-phenanthroline were identified as inhibitors and atomic absorption analysis showed that the enzyme contained Ca2+ and Zn2+. The activity of the apoenzyme could be restored with Ca2+, Zn2+, Mg2+, and Co2+. Phosphoramidon and Gly-d-Phe did not inhibit Chryseobacterium indologenes Ix9a protease. Heat inactivation did not follow first order kinetics, but showed biphasic inactivation curves. The protease has a Km of 0.813 microg. ml-1 for casein as substrate. Amino acid analysis showed that the protease contains a high amount of small amino acids like glycine, alanine, and serine, but a low concentration of methionine and no cysteine at all. Electrospray mass spectrometry of proteolysis fragments formed when insulin B chain was hydrolyzed showed cleavage at the amino terminal of leucine, tyrosine, and phenylalanine. A hydrophobic amino acid at the carboxyl donating side seems to increase the rate of reaction.

Amino Acid Sequence↗
PubMed1997

Ribosylative inactivation of rifampin by Mycobacterium smegmatis is a principal contributor to its low susceptibility to this antibiotic.

Mycobacterium smegmatis inactivates rifampin by ribosylating this antibiotic. The gene responsible for this ability was cloned and was shown to confer low-level resistance to this antibiotic (MIC increase, about 12-fold) in related organisms. A 600-bp subclone responsible for ribosylating activity and resistance carried an open reading frame of 429 bp. Targeted disruption of the gene in M. smegmatis resulted in mutants with much increased susceptibility to rifampin (MICs of 1.5 instead of 20 microg/ml) as well as the loss of antibiotic-inactivating ability. Also, disruption of this gene led to a much lower frequency of occurrence of spontaneous high-level rifampin-resistant mutants.

Amino Acid Sequence↗
PubMed1994

The 9-kDa calbindin gene of Rousettus aegyptiacus: its identification and isolation from a genomic library.

A genomic library of the fruit bat (Rousettus aegyptiacus) was constructed in lambda phage gt11. The titre of the library was determined to be 2 x 10(5) pfu/ml. The genomic library was amplified and the titre of the amplified library increased 300-fold to 7 x 10(7) pfu/ml. The library was screened by in situ hybridization techniques using a fragment of the mouse 9-kDa calbindin cDNA as a probe. Screening of 10(5) plaques yielded a positive clone. Three additional rounds of screening were performed to purify the positive. Lambda phage DNA was isolated from the positive clone and restriction digest analysis, followed by hybridization studies, was performed on these digests in order to determine the location of the bat 9-kDa calbindin gene in the insert of the lambda phage vector. Restriction maps so derived were interpreted from the published sequence for the rat 9-kDa calbindin gene and indicate the successful isolation of the 9-kDa calbindin gene of Rousettus aegyptiacus.

Animals↗
PubMed1993

Detection of the 9-kDa vitamin D-dependent calbindin gene in a fruit bat (Rousettus aegyptiacus) fibroblast cell line.

1. A fibroblast cell line was established from skin and lung tissue of the fruit bat (Rousettus aegyptiacus). 2. Genomic DNA, isolated from the fibroblast cells, was restriction digested and probed for the 9-kDa calbindin gene with a 180 base-pair fragment of mouse calbindin-D9K cDNA. Genomic DNA from rats and humans was similarly probed. 3. Hybridization and thus homology was observed between the mouse probe and DNA from the rat and the fruit bat, but not the human. 4. The results are discussed in relation to the detection of calbindin-D9K in the fruit bat despite very low circulating levels of its inducer 1,25(OH)2D3.

Animals↗
PubMed1991

Myocardial membrane cholesterol: effects of ischaemia.

Evidence has recently been presented that myocardial ischaemia is associated with a significant increased mitochondrial cholesterol content, suggesting a redistribution of cholesterol within the ischaemic cell (Rouslin et al. 1980, 1982). The aim of this study was therefore to determine the effects of different periods of ischaemia and reperfusion on the cholesterol content of myocardial mitochondria, sarcoplasmic reticulum and sarcolemma. Using the isolated perfused rat heart as experimental model, it was demonstrated that increasing periods of ischaemia (15-60 min) caused a progressive loss of cholesterol from the tissue as well as from the sarcolemma and sarcoplasmic reticulum, concomitant with a significant increase in mitochondrial cholesterol content. These compositional changes were associated with a marked increase in sarcolemmal and mitochondrial microviscosity, while that of the sarcoplasmic reticulum was reduced. To gain more insight into the mechanisms controlling intracellular cholesterol distribution, control and ischaemic hearts were perfused with either exogenous cholesterol or its precursor [U-14C]acetate as an indicator of endogenous cholesterol synthesis. Perfusion with exogenous cholesterol resulted in significant increases in the membrane cholesterol content of control hearts. However, hypoxic, low flow perfusion prevented cholesterol enrichment of the sarcolemmal and sarcoplasmic reticulum membranes, while the cholesterol content of the mitochondria was increased from 99.48 +/- 12.75 to 127.61 +/- 1.84 nmols/mg protein, indicating specific incorporation into this membrane system. Incorporation of [U-14C]acetate into cholesterol in the sarcoplasmic reticulum was increased by 120% in ischaemic conditions. However, a marked redistribution of newly synthesized cholesterol was observed within the ischaemic cell: under control conditions most of the labelled cholesterol was transferred to the sarcolemma and least to the mitochondria, while this distribution pattern was reversed in ischaemia. In view of the fact that exchange of cholesterol between membranes is affected by both phospholipid polar head-group composition and acyl chain length and saturation, it is suggested that prior ischaemia-induced membrane compositional changes might lead to intracellular cholesterol redistribution. Finally, to determine whether cholesterol loss affects sarcolemmal permeability, hearts enriched in sarcolemmal cholesterol were subjected to 15 or 30 min global ischaemia followed by reperfusion and the rate of enzyme release determined. However, enzyme release was similar in treated and untreated hearts, indicating that sarcolemmal cholesterol loss probably does not affect its permeability.

Animals↗