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M K Joshi

Publications and source records attributed to M K Joshi.

At least 19 recordsLinked to original sources
PubMed2000

On the kinetics of voltage formation in purple membranes of Halobacterium salinarium.

The kinetics of the bacteriorhodopsin photocycle, measured by voltage changes in a closed membrane system using the direct electrometrical method (DEM) of Drachev, L.A., Jasaitus, A.A., Kaulen, A.D., Kondrashin, A.A., Liberman, E.A., Nemecek, I.B., Ostroumov, S.A., Semenov, Yu, A. & Skulachev, V.P. (1974) Nature 249, 321-324 are sixfold slower than the kinetics obtained in optical studies with suspensions of purple membrane patches. In this study, we have investigated the reasons for this discrepancy. In the presence of the uncouplers carbonyl cyanide m-chlorophenylhydrazone or valinomycin, the rates in the DEM system are similar to the rates in suspensions of purple membrane. Two alternative explanations for the effects of uncouplers were evaluated: (a) the 'back-pressure' of the Deltamicro;H+ slows the kinetic steps leading to its formation, and (b) the apparent difference between the two systems is due to slow major electrogenic events that produce little or no change in optical absorbance. In the latter case, the uncouplers would decrease the RC time constant for membrane capacitance leading to a quicker discharge of voltage and concomitant decrease in photocycle turnover time. The experimental results show that the primary cause for the slower kinetics of voltage changes in the DEM system is thermodynamic back-pressure as described by Westerhoff, H.V. & Dancshazy, Z. (1984) Trends Biochem. Sci. 9, 112-117.

Bacteriorhodopsins↗
PubMed2000

Acute rhabdomyolysis and renal failure in HIV-infected patients: risk factors, presentation, and pathophysiology.

Rhabdomyolysis is a common cause of acute renal failure and may be related to a variety of predisposing factors. This entity has been increasingly recognized in HIV-infected individuals and is an important cause of morbidity and mortality. We present a series of seven HIV-positive patients admitted with rhabdomyolysis over a 5-year period; three developed acute renal failure. Infections and substance abuse were the most common risk factors identified; an average of three predisposing factors was present in each case. All patients showed resolution of creatinine phosphokinase (CPK) elevation and serum creatinine returned to the normal range in the three patients who developed renal insufficiency; however, all patients required prolonged hospitalization and one patient died of sepsis. The pathophysiological mechanisms of muscle injury in our patients are reviewed and their bearing on prognosis discussed. It is concluded that clinicians should have a high index of suspicion for the development of rhabdomyolysis in HIV-infected patients with a combination of noncompliance with medical therapy and/or substance abuse and acute infection. With comprehensive supportive care, the prognosis of acute rhabdomyolysis in this population may be reasonably good.

Acute Kidney Injury↗
PubMed1999

Regulation of the bacteriorhodopsin photocycle and proton pumping in whole cells of Halobacterium salinarium.

Single-turnover kinetics of the bacteriorhodopsin photocycle and proton-pumping capabilities of whole cells were studied. It was found that the Delta mu (tilde)H+ of the cell had a profound influence on the kinetics and components of the cycle. For example, comparing the photocycle in whole cells to that seen in PM preparations, we found that (1) the single-turnover time of the cycle was increased approximately 10-fold, (2) the mole fraction of M-fast (at high actinic light) decreased from 50 to 20%, and (3) the time constant for M-slow increased significantly. The level of Delta mu(tilde)H+ was dependent on respiration, ATP formation and breakdown, and the magnitude of a pre-existing K+ diffusion gradient. The size of the Delta mu(tilde)H+ could be manipulated by additions of HCN, nigericin, and DCCD (N,N'-dicyclohexylcarbodamide). At higher levels of Delta mu(tilde)H+, further changes in the photocycle were seen. (4) Two slower components of M-decay appeared as major components. (5) The apparent conversion of the M-fast to the O intermediate disappeared. (6) A partial reversal of an early photocycle step occurred. The photocycle of intact cells could be changed to that seen in purple membrane suspensions by the energy-uncoupler CCCP or by lysis of the cells. In fresh whole cells, light-induced proton pumping was not seen until the K+ diffusion potential was dissipated and proton accumulation facilitated by use of a K+-H+ exchanger (nigericin), respiration was inhibited by HCN, and ATP synthesis and breakdown were inhibited by DCCD. In stored cells, the pre-existing K+ diffusion gradient was diminished through slow diffusion, and only DCCD and HCN were required to elicit proton extrusion.

Bacteriorhodopsins↗
PubMed1998

Importance of specific native lipids in controlling the photocycle of bacteriorhodopsin.

Brief treatment of purple membrane (PM) with dilute detergent can cause major disruption of the BR photocycle without disrupting the trimer structure of BR [Mukhopadhyay et al. (1996) Biochemistry 35, 9245-9252]. Normal photocyle behavior can be recovered by incubating the damaged membranes with a total extract of the five types of native lipids present in PM. It is shown here that full restoration can also be obtained with combinations of squalene (SQ) and phosphatidyl glycerophosphate (PGP) which act synergistically. The addition of SQ to suboptimal levels of PGP induces complete reconstitution, principally by restoring the characteristics of the fast M intermediate, Mf (as defined in Mukhopadhyay et al. (1996) Biochemistry 35, 9245-9252). The addition of small amounts of PGP to SQ, which alone is ineffective, also induces full reconstituion. At very high levels, full reconstitution can be obtained with PGP alone. These results, in combination with earlier studies which implicate an acidic amino acid residue [Bose et al. (1997) J. Phys. Chem. B 101, 10584-10587], suggest that a crucial interaction between a particular amino acid residue and a SQ-PGP lipid complex may be essential for normal BR photocycle activity.

Bacteriorhodopsins↗
PubMed1987

Polymorphonuclear leukocyte functions in patients with acute rheumatic fever and rheumatic heart disease.

Polymorphonuclear (PMN) cell function was assessed in 30 children with active rheumatic fever (ARF) (Group I), 30 cases with active rheumatic heart disease (RHD) (Group II), 28 cases of ARF and RHD in remission (Group III) and 34 adults with quiescent RHD along with their age matched controls. All the groups showed normal spontaneous and chemotactic movement. Phagocytosis of yeast particles was significantly reduced in groups II (P less than 0.0005), III (P less than 0.025) and IV (P less than 0.005). The opsonic activity of disease sera was low in all 4 groups (P less than 0.0005). The intracellular metabolic activity was moderately elevated in Group III. Phagocytosis and opsonic activity were thus persistently low in all the groups including the remission and quiescent group.

Adolescent↗
PubMed1984

Comparative evaluation of antipyretic activity of ibuprofen and aspirin in children with pyrexia of varied aetiology.

The antipyretic activity of ibuprofen and aspirin was compared in sixteen children with pyrexia due to upper respiratory tract infection and in twelve with fever due to other causes. All 28 children received ibuprofen (7 mg/kg of body-weight) and aspirin (15 mg/kg of body-weight) in a single dose on 2 consecutive days in a crossover manner. Rectal temperature was recorded prior to and at regular intervals up to 8 hours after drug administration. Analysis of the results indicate that ibuprofen and aspirin effectively lower temperature and the two drugs are comparable in their antipyretic activity. In conclusion, significant antipyretic activity, good tolerance profile and availability in syrup form make ibuprofen a useful substitute for aspirin in children with fever.

Aspirin↗