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Biomedical subjects

M S Murthy

Publications and source records attributed to M S Murthy.

At least 37 records · Page 2Linked to original sources
PubMed1992

Purification of the medium-chain/long-chain (COT/CPT) carnitine acyltransferase of rat liver microsomes.

A procedure for the purification of the rat liver microsomal carnitine octanoyltransferase (COT) that catalyzes the reversible formation of medium-chain and long-chain acylcarnitines from acyl-coenzyme A is described. The K0.5 for L-carnitine is 0.6 mM and the K0.5 for both decanoyl-CoA and palmitoyl-CoA is 0.6 microM. The Vmax with decanoyl-CoA is approximately fourfold greater than the Vmax with palmitoyl-CoA. The enzyme is monomeric, sodium dodecyl sulfate-polyacrylamide gel electrophoresis gives a molecular weight of 50,100, and molecular sieving gives a molecular weight of 54,300. Purified COT does not cross-react with either antimitochondrial carnitine palmitoyltransferase or antiperoxisomal COT antibodies. It also does not form a covalent adduct when incubated with etomoxiryl-CoA. Microsomal COT is a different protein than either mitochondrial carnitine palmitoyltransferase or peroxisomal COT.

Acyl Coenzyme A↗
PubMed1992

Probability of causation for radiation-attributable cancer in the Indian population.

Once a cancer is diagnosed in an individual with a history of radiation exposure, it may be required to know the probability that radiation exposure was the cause of the disease. The National Institute of Health, U.S., has generated radio epidemiological tables giving probability of causation for various radiogenic cancers for the population of the U.S. In this paper, the probability of causation has been calculated for the Indian population using two models: (1) the original National Institute of Health model, and (2) direct use of Japanese constant relative risk coefficients for solid tumors. In both cases, new risk coefficients based on DS86 dosimetry and extended follow-up for 35 y have been used. Calculations with new coefficients, based on the National Institute of Health model have been extended to the American population and compared with the results for the Indian population. These values are generally higher for the Indian population than for Americans because of the lower baseline incidence rates in India. Probability of causation values based on the constant relative risk model are independent of population characteristics.

Adolescent↗
PubMed1991

Inhibition of tumor implantation at sites of trauma by plasminogen activators.

The authors report on the influence of plasminogen activators (PA) on implantation of TA3Ha mammary tumor cells in the healing hepatic wounds of syngeneic strain A mice. Intravenously injected TA3Ha cells, although they rarely metastasize to the liver, formed tumors in the hepatic wounds of a significant percent (42%, P less than 0.0001) of mice. The frequency of tumor formation declined as the interval between surgery and tumor cell inoculation was increased. Furthermore, preexposure of cells to fibrinogen, fibronectin, laminin, or peptides containing the arginine-glycine-aspartic acid-serine residues dramatically reduced the frequency of tumor formation in the hepatic wounds. These results indicate that TA3Ha cells interact with fibrinogen-related proteins in the wound to aid their attachment and growth. Because these proteins are susceptible to digestion by plasmin, PA were used in this study to examine whether administration of these drugs to the mice would modulate tumor formation in the liver wounds. Among the PA tested, human plasmin B-chain-streptokinase complex (B-SK) and recombinant tissue plasminogen activator (t-PA) inhibited tumor implantation in a dose-related manner. Administration of 900 units (U) of B-SK or 3300 U of t-PA per mouse reduced the frequency of tumor formation from 42% to 0% (P = 0.02) and 11% (P = 0.02), respectively. The B-SK was complexed with p-nitrophenyl-p-guanidinobenzoate; it did not activate the plasminogen or inhibit tumor formation in the hepatic wounds. Although urokinase activated the plasminogen, it did not inhibit tumor implantation in the hepatic wound. Heparin, an anticoagulant that prevents conversion of fibrinogen to fibrin without being fibrinolytic, had no influence on tumor formation in the hepatic wounds. The PA can generate plasmin that digests the cell attachment proteins in wounds and consequently inhibits tumor cell attachment.

Adenocarcinoma↗
PubMed1991

Influence of anoxia and respiratory deficiency on the genotoxicity of some direct-acting alkylating agents in yeast.

We have studied the influence of anoxia and respiratory deficiency (RD) in yeast on the cytotoxic and recombinogenic effects of 5 direct-acting alkylating agents, namely N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), methylnitrosourea (MNU), ethylnitrosourea (ENU), methyl methanesulphonate (MMS) and ethyl methanesulphonate (EMS). We found that the effects of both conditions parallel each other for MMS, MNNG, MNU and ENU. Both anoxia and RD did not modify the effects of MMS to any significant extent. On the other hand, anoxic and respiratory-deficient cells were found to be more resistant than euoxic and respiratory-proficient cells respectively for MNNG, MNU and ENU. In the case of EMS, which is similar to MMS in its chemical reaction with DNA, the respiratory-deficient cells were found to be more sensitive than the respiratory-proficient ones. These studies indicate that the response of anoxic and respiratory-deficient cells cannot be predicted solely on the basis of the chemical reactivity pattern of the alkylating agents. The physiological state which exists under these conditions may exert considerable influence on the cellular response.

Alkylating Agents↗
PubMed1991

Tritium metabolism in man.

Tritium metabolism in human beings was studied in volunteers who had exposure to tritiated water accidentally, by measuring the organically bound tritium with liquid scintillation counter, in sperms and plasma proteins. 2% of the initial urinary tritium specific activity was incorporated as bound tritium in sperms. In plasma proteins, on the 20th day of exposure, tritium bound in globulin was 3 times higher than that of albumin, tritium bound in globulin was 3 times higher than that of albumin.

Adult↗
PubMed1991

Naphthol and lens.

Alpha and beta naphthols, the metabolites of naphthalene, a cataractogenic agent, was tested for it's effect on sheep lens proteases and their inhibitors. It reduced protease activities, not that of inhibitor activities of lens proteins. It also increased the efflux of free amino acid from lenses which was retarded by a high concentration of tissue galactose.

Amino Acids↗
PubMed1990

Characterization of a solubilized malonyl-CoA-sensitive carnitine palmitoyltransferase from the mitochondrial outer membrane as a protein distinct from the malonyl-CoA-insensitive carnitine palmitoyltransferase of the inner membrane.

By using octyl glucoside in the presence of glycerol, it is possible to obtain a solubilized malonyl-CoA-sensitive carnitine palmitoyltransferase (CPTo) from the outer membranes of rat liver mitochondria. H.p.l.c. on hydroxyapatite column has now allowed a clear separation of the CPTo from the malonyl-CoA-insensitive CPT activity of the inner membranes (CPTi). The separated CPTo activity showed inhibition by low micromolar concentrations of malonyl-CoA, 2-tetradecylglycidyl-CoA and etomoxir-CoA. On solubilization and fractionation, the CPTo rapidly lost activity, unlike the relatively stable CPTi activity. Reconstitution into asolectin liposomes enhanced the activity and the malonyl-CoA-sensitivity of the CPTo fractions, whereas it had no such effect on the activity or malonyl-CoA insensitivity of the CPTi fractions. A polyclonal antibody raised against the malonyl-CoA-insensitive enzyme, purified from the inner membranes, precipitated the CPTi activity, but showed no reactivity with the CPTo fractions. In Western blots, the above antibody did not react with any polypeptide of the CPTo fractions. Incubation of the outer-membrane preparations with [3H]etomoxir, in the presence of ATP and CoA, led to labelling of a 90 kDa polypeptide that in the above hydroxyapatite chromatography was eluted in the same region as the CPTo. No such polypeptide labelling was seen in the CPTi fractions. With heart and skeletal-muscle mitochondria, the correspondingly labelled polypeptide was of about 86 kDa. These results show that the CPTo and CPTi are distinct proteins, that a subunit of 90 kDa for liver and 86 kDa for muscle constitutes a component of their respective CPTo systems, and that the 66 kDa subunit of the CPTi does not constitute a part of the CPTo system.

Acyl Coenzyme A↗
PubMed1990

Freeze-thawing causes masking of membrane-bound outer carnitine palmitoyltransferase activity: implications for studies on carnitine palmitoyltransferases deficiency.

Carnitine-dependent transport of fatty acids into mitochondria is believed to require participation of two carnitine palmitoyltransferase (CPT) activities, one outer, overt (CPTo) and the other inner, latent (CPTi). For exposing the CPTi and monitoring of the total CPT activity, freeze-thawing and sonication have been frequently employed as membrane-disruptive procedures, particularly when examining for CPT-deficiency diseases. Our evaluations have shown, however, that freeze-thawing and sonication yield misleading data for both the CPT activities owing to their previously unrecognized masking and unmasking effects on CPT activities. Formation of vesicular/sheath structures with mixed membrane orientation that prevents the access of medium substrate to enzymes on both aspects of the membrane at the same time appears responsible for these results. That such procedures can yield inexact data when monitoring the latency and sidedness of other membrane-bound biocatalysts as well needs to be recognized. We show that in muscle mitochondria also, a malonyl-CoA-inhibitable CPTo activity resides in the outer membrane, while a malonyl-CoA-insensitive, CPTi, activity is present in the inner membrane. Our results rationalize why Zierz and Engel ((1987) Neurology 37, 1785) were unable to obtain evidences for a latent CPT activity in mitochondria particularly of muscles. Although simple methods to allow an unambiguous quantitation of the two CPT activities in tissue extracts remain unavailable, evaluation of the possibility that two different CPT deficiencies occur appears justified.

Acyltransferases↗
PubMed1990

Acyl-CoA chain length affects the specificity of various carnitine palmitoyltransferases with respect to carnitine analogues. Possible application in the discrimination of different carnitine palmitoyltransferase activities.

The activities of carnitine palmitoyltransferases (CPTs) of mitochondrial outer and inner membranes and of peroxisomes have been studied with carnitine analogues, namely DL-thiolcarnitine, DL-sulphocarnitine and L-aminocarnitine, using palmitoyl-CoA or octanoyl-CoA as co-substrate. With sulphocarnitine, both of the mitochondrial CPTs and the malonyl-CoA-sensitive CPT of peroxisomes showed appreciable activity with palmitoyl-CoA, but relatively lower activity when octanoyl-CoA was the co-substrate. The soluble CPT of peroxisomes did not show any activity with sulphocarnitine in the presence of either acyl-CoA. With thiolcarnitine, all of the CPTs showed more activity with palmitoyl-CoA than with octanoyl-CoA. None of the CPTs showed any activity with aminocarnitine and palmitoyl-CoA, but when the acyl donor was octanoyl-CoA, both of the malonyl-CoA-sensitive CPT enzymes showed considerable activity, unlike the malonyl-CoA-insensitive CPT isoenzymes. Aminocarnitine inhibited palmitoylcarnitine formation by both of the mitochondrial CPTs and by the CPT of gradient-purified peroxisomes, but the purified peroxisomal soluble CPT was not inhibited. These results show that the interaction of CPT enzymes with carnitine analogues, as substrates or inhibitors, is influenced by the chain length of the acyl-CoA substrate, and that the use of the appropriate carnitine analogue and acyl-CoA is likely to be useful for the discrimination of the various CPT activities in CPT deficiency disorders.

Acyl Coenzyme A↗
PubMed1989

Partial nephrectomy in mice with milliwatt carbon dioxide laser and its influence on experimental metastasis.

We have developed a surgical model to perform partial nephrectomy in mice using the milliwatt CO2 laser and have used this model for studying the influence of the sequel of surgery on experimental tumor metastasis. Strain A mice were subjected to partial nephrectomy using the milliwatt CO2 laser. The surgical procedure was time efficient, the blood loss was minimal, and the postoperative mortality was 6%. Immediately after surgery, the wound consisted of a superficial layer of charring and a deeper layer of thermal damage (coagulative necrosis). The wound healing was completed within 30 days and was accompanied by fibroblast infiltration and tubular regeneration but minimal inflammatory response. Seventy surgical mice were injected I.V. with TA3Ha murine mammary adenocarcinoma cells at different intervals (immediately to 30 days) after surgery. Among 38 mice inoculated with tumor cells immediately or up to 3 days after surgery, 18 (47%) showed histologically confirmed tumors at the site of surgical trauma. None of the 38 unoperated kidneys showed any evidence of tumor. This difference is statistically significant at a P value of less than 0.001. As the interval between surgery and tumor inoculation was increased to 7, 15, and 30 days, the frequency of tumor formation at the site of surgery decreased to 20% (2/10), 14% (2/14), and 0% (0/8), respectively. The results demonstrate that a) partial nephrectomy in mice is feasible with minimal mortality or apparent morbidity, b) the laser-induced surgical trauma favors implantation and growth of tumors, c) the frequency of tumor formation is related to the stage of wound healing, and d) the tumors are anatomically related to the healing wound but do not invade into the parenchymal tissue.

Adenocarcinoma↗
PubMed1988

Metabolic fate of N1-methyladenine in yeast auxotrophic to adenine.

The metabolic fate of N1-methyladenine in yeast with respect to its incorporation into RNA has been studied. Chromatographic analysis of the PCA-soluble and -insoluble fractions of cells grown in the combined presence of adenine and 3H-labeled N1-methyladenine show that (a) N1-methyladenine can enter the cells, (b) however, it is very poorly utilized by the salvage pathway for nucleic acid synthesis and (c) the inhibition occurs probably at the first stage of conversion of the methylated base to the corresponding nucleotide.

Adenine↗
PubMed1988

ATP-Mg2+ reversal of the salt activation of membrane bound carnitine palmitoyltransferase activities of liver mitochondria.

The carnitine palmitoyltransferase (CPT) activities of the outer and the inner membranes of rat liver mitochondria were markedly activated by increase in the ionic strength of the assay medium. ATP at physiological concentrations in the presence of Mg2+ effectively reversed the above effect with octanoyl-CoA, but not with palmitoyl-CoA, as a substrate. Other nucleotides were unable to substitute for ATP. This ATP-Mg2+ effect on the CPT activity was not seen with mitochondria of heart or of skeletal muscles. The remarkable nucleotide, substrate and tissue specificity of these effects indicate that the above phenomenon may be functional in vivo to regulate the ability of liver mitochondria to utilize medium chain fatty acids via the carnitine-dependent route.

Acyltransferases↗