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Biomedical subjects

M B Rao

Publications and source records attributed to M B Rao.

At least 37 records · Page 2Linked to original sources
PubMed1996

Molecular and industrial aspects of glucose isomerase.

Glucose isomerase (GI) (D-xylose ketol-isomerase; EC. 5.3.1.5) catalyzes the reversible isomerization of D-glucose and D-xylose to D-fructose and D-xylulose, respectively. The enzyme has the largest market in the food industry because of its application in the production of high-fructose corn syrup (HFCS). HFCS, an equilibrium mixture of glucose and fructose, is 1.3 times sweeter than sucrose and serves as a sweetener for use by diabetics. Interconversion of xylose to xylulose by GI serves a nutritional requirement in saprophytic bacteria and has a potential application in the bioconversion of hemicellulose to ethanol. The enzyme is widely distributed in prokaryotes. Intensive research efforts are directed toward improving its suitability for industrial application. Development of microbial strains capable of utilizing xylan-containing raw materials for growth or screening for constitutive mutants of GI is expected to lead to discontinuation of the use of xylose as an inducer for the production of the enzyme. Elimination of Co2+ from the fermentation medium is desirable for avoiding health problems arising from human consumption of HFCS. Immobilization of GI provides an efficient means for its easy recovery and reuse and lowers the cost of its use. X-ray crystallographic and genetic engineering studies support a hydride shift mechanism for the action of GI. Cloning of GI in homologous as well as heterologous hosts has been carried out, with the prime aim of overproducing the enzyme and deciphering the genetic organization of individual genes (xylA, xylB, and xylR) in the xyl operon of different microorganisms. The organization of xylA and xylB seems to be highly conserved in all bacteria. The two genes are transcribed from the same strand in Escherichia coli and Bacillus and Lactobacillus species, whereas they are transcribed divergently on different strands in Streptomyces species. A comparison of the xylA sequences from several bacterial sources revealed the presence of two signature sequences, VXW(GP)GREG(YSTAE)E and (LIVM)EPKPX(EQ)P. The use of an inexpensive inducer in the fermentation medium devoid of Co2+ and redesigning of a tailor-made GI with increased thermostability, higher affinity for glucose, and lower pH optimum will contribute significantly to the development of an economically feasible commercial process for enzymatic isomerization of glucose to fructose. Manipulation of the GI gene by site-directed mutagenesis holds promise that a GI suitable for biotechnological applications will be produced in the foreseeable future.

Aldose-Ketose Isomerases↗
PubMed1995

Prevalence of diabetes in the young in south India.

Students from nine schools and one college in Madras city, were screened for diabetes by oral glucose tolerance test. The criteria recommended by the World Health Organization was adopted to classify glucose tolerance. Among 3,515 students, between 5 and 19 years of age, participated in this survey, 1982 (56.4%) were males and 1.533 were (43.6%) females. Family history of diabetes was positive in 302 (8.6%) students. There was no overt case of diabetes of any type. Three (0.09%) males had renal glycosuria. It is therefore concluded that insulin-dependent diabetes, non-insulin dependent diabetes or any other type of diabetes in the young is rare in South India.

Adolescent↗
PubMed1992

Characterization and sequencing of an active-site cysteine-containing peptide from the xylanase of a thermotolerant Streptomyces.

The kinetics of chemical modification of the xylanase from a thermotolerant Streptomyces T7 indicated the involvement of 1 mol of cysteine residue/mol of enzyme [Keskar, Srinivasan & Deshpande (1989) Biochem. J. 261, 49-55]. The chromophoric reagent N-(2,4-dinitroanilino)maleimide (DAM) reacts covalently with thiol groups of xylanase with complete inactivation. Protection against inactivation was provided by the substrate (xylan). The purified xylanase that had been modified with DAM was digested with pepsin and the peptides were purified by gel filtration followed by peptide mapping. The active-site peptide was distinguished from the other thiol-containing peptides by comparison of the peptides generated by labelling the enzyme in the presence and in the absence of the substrate. The peptide mapping of the modified enzyme in the absence of xylan showed three yellow peptides, whereas in the presence of xylan only two yellow peptides were detected. The active-site peptide protected by the substrate failed to form the complex with DAM. The modified active-site peptide was isolated and sequenced. Gas-phase sequencing provided the following sequence: Ser-Val-Ile-Met-Xaa-Ile-Asp-His-Ile-Arg-Phe. This is the first report on the isolation and sequencing of the active-site peptide from a xylanase. The comparison of reactive cysteine-containing peptide sequence with the catalytic regions of other glucanases revealed the presence of a conserved aspartic acid residue.

Amino Acid Sequence↗
PubMed1986

Hyperglycemia-induced activation of human erythrocyte aldose reductase and alterations in kinetic properties.

Incubation of human erythrocytes with varying concentrations of glucose resulted in a several-fold increase in aldose reductase (alditol:NADP+ 1-oxidoreductase, EC 1.1.1.21) activity as determined by the rate of NADPH oxidation and the rate of sorbitol formation. As compared to aldose reductase from human erythrocytes not incubated with glucose (native enzyme), aldose reductase from 30 mM glucose-incubated erythrocytes (activated enzyme) exhibited altered kinetic and inhibition properties. Native enzyme showed biphasic kinetics with substrates (glucose and glyceraldehyde), was strongly inhibited by 15 microM ADP, 1,3-diphosphoglycerate, 2,3-diphosphoglycerate and 3-phosphoglycerate, and aldose reductase inhibitors such as sorbinil and alrestatin. The activated enzyme, on the other hand, exhibited monophasic kinetics, low Km for substrates, was not inhibited by the phosphorylated intermediates, and was less susceptible to inhibition by aldose reductase inhibitors. In erythrocytes of the diabetic subjects, we have found an excellent correlation between aldose reductase activity and plasma glucose levels and have observed that whenever the blood glucose level was higher than 15 mM, all of the erythrocyte aldose reductase was present in the activated form and exhibited properties similar to those observed with aldose reductase obtained from 30 mM glucose-incubated erythrocytes.

Aldehyde Reductase↗
PubMed1986

Primary hypothyroidism in chronic renal failure.

Serum thyroid hormone concentrations have been measured in 8 patients with chronic renal failure (CRF) who are currently enrolled on a chronic hemodialysis program. Three of these patients were diagnosed to be suffering from coexistent primary hypothyroidism whereas the other 5 were considered euthyroid. There was a variable decline in serum thyroid hormone levels in both groups. However, the serum TSH response to TRH was normal or blunted in the euthyroid group but was characteristically brisk in subjects with CRF and coexistent primary hypothyroidism. The TRH test may be useful in the diagnosis of primary hypothyroidism coexistent with CRF.

Adult↗
PubMed1981

Vasopressin and oxytocin content of human fetal brain at different stages of gestation.

Pituitaries from 38 human fetuses and 5 microdissected hypothalamic areas from each of 14 fetuses were assayed for vasopressin and oxytocin. The fetuses were between 15 and 34 weeks of gestation. Vasopressin and oxytocin were found in all the pituitary glands and all the hypothalamic areas studied. A trend of increasing content of both hormones was found in the pituitary gland towards the end of gestation with a marked increase in vasopressin/oxytocin ratio. The human fetus synthesizes oxytocin and vasopressin at least from 15 weeks of gestation and the presence of both hormones in the hypothalamus is not limited to the supraoptic and paraventricular nuclei.

Arginine Vasopressin↗
PubMed1981

Incidence of tempero-mandibular joint pain dysfunction syndrome in rural population.

The incidence and clinical course of the tempero-mandibular joint dysfunction syndrome was studied among 1187 subjects over the age of 16, who attended the rural dental consultations held at various places in the State of Karnataka, India. The study revealed an incidence of 20.3%. Contracy to earlier reports, the incidence was higher in males than in females and more married females were affected than unmarried. Clicking appeared to be the predominant symptom in all age groups. The incidence of pain increased with age. Of all patients 43.75% were not aware of a clicking joint; 53.7% persons with clicking and 14% with pain were not disturbed by their symptoms. The findings of the study failed to establish any relationship between unilateral missing teeth and the occurrence of the pain dysfunction syndrome (PDS). The chewing habits (betel leaf, tobacco, betel nut) which are prevalent in India appeared to have no effect on the incidence of PDS. It is suggested that more epidemiological studies should be carried out in different parts of the world with varying social, political and economic systems to enable better understanding of the global incidence of PDS.

Adolescent↗