Biomedical subjects

L H Mei

Publications and source records attributed to L H Mei.

3 recordsLinked to original sources

PubMed2001

Controlled release of biomolecules from temperature-sensitive hydrogels prepared by radiation polymerization.

Poly(acryloyl-L-proline methyl ester)-based hydrogels containing 1 and 5% of a crosslinking agent were studied as drug delivery systems. The drug loading properties were investigated by matrix incubation into solutions containing biomolecules with molecular weight ranging between 300 and 65,000 Da. The loading yield was found to depend on both the crosslinking degree and the molecular weight of the drug. In vitro release studies were carried out with both swollen and dry matrices loaded with gentamicin, isoniazid and insulin. Gentamicin and isoniazid were released by a bimodal Fickian diffusion with a remarkable burst that was found to depend on both matrix crosslinking degree and physical state. In vivo, the subcutaneous implantation into mice of the isoniazid loaded matrices allowed for an efficient drug release for 800 h. In vitro insulin was released from the swollen matrices for 1500 h by diffusional Fickian mechanism while the dry ones displayed a lag time followed by Fickian diffusion release. The subcutaneous implantation of the insulin-loaded matrices into diabetic mice induced a remarkable decrease in the glucose concentrations in blood. In particular, the dry 1% matrices were found to maintain a low glucose level for 700 h.

Animals↗

PubMed1992

Supports for enzyme immobilization.

Macroporous silica gel, prepared from sodium silicate and hydrochloric acid, one grade of diatomaceous earth (celite 545) and nonporous glass were analyzed in terms of pore size by the mercury intrusion pressure method. The alkylamine derivatives of the above materials were examined for their suitability as supports for enzyme immobilization, using the enzyme glucose oxidase. The effectiveness of the immobilized enzyme was compared in relation to the free enzyme and particle size of the carrier. The immobilized enzyme exhibited a broader range of optimum pH and greater thermal stability, among some properties considered.

Enzymes, Immobilized↗

PubMed1991

The conformation of SecA, as revealed by its protease sensitivity, is altered upon interaction with ATP, presecretory proteins, everted membrane vesicles, and phospholipids.

Interactions between SecA and cellular components involved in the translocation of secretory proteins across the cytoplasmic membrane of Escherichia coli were studied by examining changes in the sensitivity of SecA to staphylococcal protease V8. In the presence of ATP, the amino-terminal 95-kDa portion of the SecA molecule became highly resistant to V8 digestion. Adenosine 5'-(gamma-thio)triphosphate (ATP gamma S) and ADP were as effective as ATP. For the effect, ATP could be partly replaced by CTP and UTP, but not GTP, as in the case of the protein translocation reaction. In the presence of proOmpA, a presecretory protein, on the other hand, SecA became more sensitive to V8 digestion. The signal peptide region was involved in this effect. The V8-digestion profile in the presence of both proOmpA and ATP or ADP was the same as that in the presence of proOmpA alone. Consistently, proOmpA-induced discharge of ADP or ATP gamma S from SecA was observed by means of flow dialysis. SecA-deprived everted membrane vesicles and an E. coli phospholipid mixture were also effective in making SecA more sensitive to V8 digestion. Among the phospholipids, phosphatidylglycerol and cardiolipin were effective, whereas phosphatidylethanolamine was not. It is suggested that SecA directly interacts with these cellular components and the interactions result in changes in the conformation of SecA. The physiological significance of such interactions in protein secretion is discussed.

Adenosine Triphosphatases↗