Biomedical subjects

J B Joshi

Publications and source records attributed to J B Joshi.

17 recordsLinked to original sources

PubMed1998

Role of hydrodynamic shear on activity and structure of proteins.

Proteins are important products used in industry. They may be enzymes which catalyze different reactions or they may be required for their biological activities as hormones, growth factors or therapeutics. During production and recovery, proteins are subjected to fluid forces which arise due to operations such as stirring, pumping and centrifugation. The resulting hydrodynamic shear forces may cause damage to the large molecular weight proteins, resulting in denaturation and inactivation of the protein. This is a major concern as it affects the overall efficiency of protein recovery and final yield of the product. A considerable amount of research has been devoted to studying the effects of hydrodynamic shear stress on proteins, especially with respect to the enzymes. Enzymes are subjected to shear stresses during their production in fermentors, during isolation and purification steps in downstream operations and also during their use in enzyme reactors, especially if stirred reactors are employed to perform enzyme catalysed reactions. The present review discusses the effects of fluid shear stress on proteins including enzymes. A brief description on deactivation has been included in order to understand the effect of shear on the deactivation kinetics of proteins. The model systems used to subject proteins to shear and some unit operations during protein processing or use wherein they are exposed to shear stresses have also been presented. The significance of shear effects in designing bioprocesses involving shear sensitive biocatalysts as well as suggestions for future work have also been given.

Chemical Precipitation↗

PubMed1997

Transactivation of proenkephalin gene by HTLV-1 tax1 protein in glial cells: involvement of Fos/Jun complex at an AP-1 element in the proenkephalin gene promoter.

The human T-cell lymphotropic virus type 1 (HTLV-1), an etiologic agent for adult T-cell leukemia, is strongly associated with tropical spastic paraparesis, a chronic neurological disease. The HTLV-1 genome encodes a protein, tax1, an autoregulator of enhanced viral RNA transcription, that also transactivates/represses certain cellular gene promoters. Enkephalins are opioid peptides that function as neurotransmitters and neuroimmunomodulators. We earlier reported that the proenkephalin gene is transactivated by tax1 protein in glial cells. The nucleotide sequence upstream of -190 base pairs in the proenkephalin gene promoter is necessary for maximal transactivation by tax1 while the sequence downstream of -190 bp confers modest activation by tax1. We investigated the cellular transcription factors in tax1 expressing glial cells that associate with the proenkephalin promoter and herein demonstrate the enhanced interaction and involvement of c-Fos/c-Jun proteins in the complexes formed at the AP-1 site. The HTLV-1 tax1 expressing stable glial cell lines produced functional tax1 protein that increased the expression of endogenous proenkephalin gene. The comparative electrophoretic mobility shift and 'supershift' analysis using specific antibodies indicated the enhanced presence of c-Fos and c-Jun proteins in the DNA: protein complex formed at the AP-1 site. The c-Fos protein expression significantly increased in the tax1 expressing glial cells. The tax1 induced c-Fos protein levels and the concurrently increased association of c-Fos/c-Jun transcription factors at the AP-1 site imply a strong functional significance in the activation of proenkephalin gene expression in tax1 expressing glial cells.

Animals↗

PubMed1995

Molecular cloning and chromosomal mapping of the mouse cyclin-dependent kinase 5 gene.

Cyclin-dependent kinase 5 (Cdk5) is predominantly expressed in neurons. In vitro, Cdk5 purified from the nervous tissue phosphorylates both high-molecular-weight neurofilament and microtubule-associated tau. The mouse gene encoding Cdk5 (Cdk5) was found to be 5 kb in length and divided into 12 exons. All of the exon-intron junctions matched the expected consensus sequence with the exception of the splice junction for intron 9, which has AT and AC dinucleotides instead of the usual GT and AG bordering sequence. In the 5'-flanking region of mouse Cdk5, several putative promoter elements were present, including AP1, Sp1, PuF, and TATA motifs. A metal regulatory element was also identified at position -207 to -201. Nucleotide sequence analysis of mouse Cdk5 showed high identity to the homologues of other vertebrate species, indicating that this kinase is highly conserved during evolution. Mouse Cdk5 was mapped to the centromeric region of mouse chromosome 5.

Amino Acid Sequence↗

PubMed1992

Transactivation of the proenkephalin gene promoter by the Tax1 protein of human T-cell lymphotropic virus type I.

Human T-cell lymphotropic virus type I (HTLV-I), an etiologic agent for adult T-cell leukemia, is strongly associated with certain neurological diseases. The HTLV-I genome encodes a protein, Tax1, that transactivates viral gene transcription. CD4-positive T helper lymphocytes express the proenkephalin gene, and enkephalins have been implicated as neuroimmunomodulators. We have investigated the effect of Tax1 on the proenkephalin gene promoter in C6 rat glioma cells and demonstrated its transactivation. Analysis using 5' deletion mutants of the promoter region showed that sequences upstream of base pair -190 are necessary for maximal transactivation. Forskolin, a cAMP modulator, synergistically increased Tax1-mediated transactivation of the proenkephalin promoter. Neither Tax1 transactivation alone nor Tax1/cAMP synergism exclusively involved cAMP-responsive elements. Endogenous proenkephalin gene expression increased in Tax1-expressing C6 cells. Since HTLV-I infects lymphocytes, which express proenkephalin mRNA, Tax1 transregulation of proenkephalin expression may provide bidirectional communication between the nervous and immune systems in HTLV-I-related diseases.

Animals↗

PubMed1990

Continuous counter-current two-phase aqueous extraction.

Continuous counter-current column operation provides operating convenience for contacting two-phase aqueous partitioning systems for protein extraction. We discuss in detail the important parameters for designing spray, packed, plate and York-Scheibel columns for protein recovery using both polymer-polymer and polymer-salt two-phase aqueous systems. We compare the various contractors for their operating and extraction efficiency. The work also provides a step-by-step design procedure and specific recommendations for future data needs.

Methods↗

PubMed1989

Influence of the mode of preparation on the distortion and consistency of homologous costal cartilage implants.

Nasal implants of autologous costal cartilage have an undesirable tendency to distortion. This tendency may be reduced by the process of devitalization, which occurs in the preparation of homologous costal cartilage for storage in a tissue bank. An in vitro study has been undertaken, utilizing five common methods of cartilage preparation (cialit, ethyl alcohol, formalin, glutaraldehyde and irradiation) to determine whether there is any significant variation in the degree of distortion which occurred and any variation in cartilage consistency. We conclude that all of the methods evaluated would produce banked homologous costal cartilage with an equally low incidence of distortion but implants are less readily carved from cartilage stored in cialit.

Cartilage↗

PubMed1983

Correlation between nuclear glucocorticoid receptor levels and casein gene expression in murine mammary gland in vitro.

The relationship between nuclear binding of glucocorticoid-receptor complex and casein gene expression was studied in organ culture of the whole mammary gland of the mouse. Pyridoxal 5'-phosphate was used as a modulatory agent for measuring nuclear binding of the receptor complex. Addition of 2 mM and 5mM pyridoxal-5'-P in the medium (Waymouth's MB752/1) resulted in 4- and 12-fold increase of its concentration in the glands incubated with insulin, prolactin, and hydrocortisone. Pyridoxal-5'-P also caused a 52% and 92% inhibition of nuclear binding of [3H]dexamethasone in the glands at 2 mM and 5 mM concentration in the presence of the same hormones in the medium. Corresponding to the reduced nuclear binding of the receptor complex casein mRNA levels, measured by a specific cDNA probe was reduced 86% and over 90% in the glands exposed to 2 mM and 5 mM pyridoxal-5'-P, respectively, in presence of insulin, prolactin, and hydrocortisone in the medium. Withdrawal of pyridoxal-5'-P from the medium restored nuclear binding of the receptor complex near the level of control glands incubated only with the hormones. mRNA casein levels also increased in the gland in the pyridoxal-5'-P-free medium containing the same hormones. This indicates that pyridoxal-5'-P does not alter the specific hormone responsiveness of the mammary cells and its action mediated at the level of the glucocorticoid receptor can influence hormone-inducible expression of the casein genes. Thus, glucocorticoid plays a major role in the multiple hormone regulation of the milk protein gene(s). The findings also suggest that the breast tissue concentration of the vitamin B6 derivative may influence the physiology of lactation in nursing mothers.

Animals↗

PubMed1979