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Biomedical subjects

R K Sharma

Publications and source records attributed to R K Sharma.

At least 19 recordsLinked to original sources
PubMed1992

Novel bovine heart calmodulin-dependent protein kinase which phosphorylates a high molecular weight calmodulin-binding protein.

A novel calmodulin-dependent protein kinase has been isolated from bovine cardiac muscle by successive chromatography on DEAE-Sepharose 6B, Calmodulin-Sepharose 4B affinity and Sepharose 6B chromatography columns. The protein kinase was shown by gel filtration chromatography to have a molecular mass of 36,000 daltons. The highly purified protein kinase stoichiometrically phosphorylated the high molecular weight calmodulin-binding protein from cardiac muscle [Sharma RK (1990) J Biol Chem 265, 1152-1157] in a Ca2+/calmodulin-dependent manner. The phosphorylation resulted in the maximal incorporation of 1 mol of phosphate/mol of the high molecular weight calmodulin-binding protein. Other Ca2+/calmodulin-dependent protein kinases failed to phosphorylate the high molecular weight calmodulin-binding protein. The distinct substrate specificity of this protein kinase indicates that it is not related to the known calmodulin-dependent protein kinases and therefore constitutes a novel protein kinase.

Animals↗
PubMed1992

Demonstration of multiple forms of bovine brain myristoyl CoA:protein N-myristoyl transferase.

Four distinct N-myristoyl transferase (NMT) activity peaks, designated I, II, III, and IV, were separated from the cytosolic fraction of bovine brain by DEAE-Sepharose column chromatography. Peaks I, II, III and IV were characterised biochemically with respect to substrate specificity: with cAMP-dependent protein kinase and pp60src derived peptides, and by their apparent molecular mass. The apparent molecular mass of peaks I, II, III and IV were 190 kDa, 224 kDa, 390 kDa and 76 kDa, respectively. These results indicate that bovine brain contains multiple forms of NMT.

Acyltransferases↗
PubMed1992

Nitroprusside-sensitive and insensitive guanylate cyclases in retinal rod outer segments.

Rod outer segments of retina contain guanylate cyclase activity both in the cytosol and membrane fractions. Though the activity in the cytosol is a small fraction of the total activity, it is highly activated by nitroprusside, a nitric oxide generating agent. The membrane guanylate cyclase on the other hand is unaffected by nitroprusside both before and after solubilization. The effects of nitroprusside or nitric oxide on photoreceptor function should therefore be mediated by the cytosolic and not the membrane guanylate cyclase.

Animals↗
PubMed1992

A structural motif that defines the ATP-regulatory module of guanylate cyclase in atrial natriuretic factor signalling.

Atrial natriuretic factor (ANF)-dependent guanylate cyclase is a single-chain transmembrane-spanning protein, containing an ANF receptor and having catalytic activity. ANF binding to the receptor domain activates the catalytic domain, generating the second messenger cyclic GMP. Obligatory in this activation process is an intervening step regulated by ATP, but its mechanism is not known. Through a programme of site-directed and deletion mutagenesis/expression studies, we report herein the identity of a structural motif (Gly503-Arg-Gly-Ser-Asn-Tyr-Gly509) that binds ATP and amplifies the ANF-dependent cyclase activity; this, therefore, represents an ATP-regulatory module (ARM) of the enzyme, which plays a pivotal role in ANF signalling.

Adenosine Triphosphate↗
PubMed1992

Genetically tailored atrial natriuretic factor-dependent guanylate cyclase. Immunological and functional identity with 180 kDa membrane guanylate cyclase and ATP signaling site.

Biochemical and immunological studies have established that one of the signal transducers of atrial natriuretic factor (ANF) is a 180 kDa membrane guanylate cyclase (180 kDa mGC), which is also an ANF receptor; obligatory in the transduction process is an intervening ATP-regulated step, but its mechanism is not known. GC alpha is a newly discovered member of the guanylate cyclase family whose activity is independent of the known natriuretic peptides, and the enzyme is not an ANF receptor. The genetically tailored GC alpha, GC alpha-DmutGln338Leu364, however, is not only a guanylate cyclase but also an ANF receptor and is structurally and functionally identical to the cloned wild-type ANF receptor guanylate cyclase, GC-A. We now report that the ANF-dependent guanylate cyclase activity in the particulate fractions of cells transfected with GC alpha-DmutGln338Leu364 was inhibited by the 180 kDa mGC polyclonal antibody, and with this antibody probe it was possible to purify the 130 kDa expressed receptor; the hormone-dependent cyclase activity of this receptor was exclusively dependent upon ATP; and through site-directed mutational studies with GC alpha mutants, the signaling sequence that defines ATP binding site was identified. We thus conclude that 180 kDa mGC and the mutant protein are immunologically similar, both proteins are linked to the ANF signal in the generation of cyclic GMP synthesis; and in both the ligand binding and catalytic activities are bridged through a defined ATP binding module.

Adenosine Triphosphate↗
PubMed1992

Three immunologically similar atrial natriuretic factor receptors.

One of the atrial natriuretic factor (ANF) receptors is a 180 kDa protein (180 kDa mGC) which possesses the extraordinary characteristic of being bifunctional: it is both a receptor and a guanylate cyclase. In addition to the 180 kDa mGC, there exists another 120-130 kDa protein which is also bifunctional and a 120 kDa disulfide-linked dimeric cell surface protein that is an ANF receptor, but is not a part of guanylate cyclase. A fundamental question that needs to be resolved is: Are these three apparently biochemically distinct ANF receptors structurally similar? With the aid of affinity crosslinking techniques, a highly specific antibody to the 180 kDa mGC, and GTP-affinity techniques, we now demonstrate the presence of three immunologically similar proteins in rat adrenal gland and testes. These proteins migrate as 180 kDa, 130 kDa and 65 kDa under denaturing sodium dodecyl sulfate polyacrylamide gel electrophoresis and specifically bind ANF, raising one or more of the following possibilities about their relationships: 1) Degradation of 180 kDa to 130 kDa and 65 kDa occurs during purification; 2) 180 kDa bears a precursor-product relationship with 130 kDa and 65 kDa, suggesting the role of a protease in the processing procedure; 3) these proteins are a result of gene splicing; or 4) they are the products of three separate, but very closely related genes.

Adrenal Glands↗
PubMed1992

Effects of STS-557 and 20 Aet-1 on sperm functions and serum level of testosterone in bonnet monkey (Macaca radiata).

Treatment of adult male bonnet monkeys with STS-557 (17 alpha-cyanomethyl 17 beta-hydroxy estra-4, 9(10)-dien-3-one; 12 mg/monkey daily for 15 weeks; i.m.) reduced the sperm count from the 9th week, leading close to azoospermia on the 2nd post-treatment week which persisted until the 10th post-treatment week and normalcy was restored on the 13th post-treatment week. The sperm motility was reduced from the 9th week of treatment to 8th post-treatment week. The fertilizing ability of spermatozoa (formation of swollen sperm head or pronuclei in zona-free hamster eggs) was abolished from the 8th week of treatment to the 7th post-treatment week. The serum level of testosterone was reduced from the 2nd to 12th week of treatment (data on subsequent weeks were not collected). When 20 Aet-1 (testosterone-trans-4-n butyl cyclohexyl carboxylate; 40 mg/monkey, single; i.m.) was administered on the first day of STS-557 treatment, the sperm count was reduced from the 10th week, with near azoospermia ensuing on the 13th week which continued until the 8th post-treatment week; recovery was observed on the 12th post-treatment week. The motility was low from the 8th week of treatment to 6th week after withdrawal of treatment. The fertilizing ability of spermatozoa was abolished from the 8th week to the 12th week of treatment (data on last week of treatment were not collected). The serum level of testosterone was maintained within normal range except on the 2nd, 6th and 12th week of treatment. 20 Aet-1 alone had no significant effect on these parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Nonischemic intussusception in childhood.

The classical presentation of intussusception consisting of severe abdominal pain, bloody stool, and a palpable abdominal mass leads to the correct diagnosis in majority of the patients. However, an atypical presentation often results in a delayed diagnosis as is commonly seen in nonischemic intussusception. The nonischemic intussusception is a distinct clinical entity that is characterized by a long history of less severe symptoms commonly noticed in older children. The incidence of diarrhea in this group is higher than in the acute variety of intussusception. This variant of intussusception requires a high degree of suspicion for the diagnosis in atypical clinical presentation. The present study summarises our experience treating 31 such cases of nonischemic intussusception during a period of 25 years from 1966 to July 1990.

Child↗
PubMed1992

Reconstruction of a major abdominal and chest wall defect using latissimus dorsi and extended deep inferior epigastric artery flap.

Large defects of the chest and abdominal cavity are a challenging reconstructive problem. We present reconstruction of a major chest and abdominal wall defect in a patient who had recurrent chondrosarcoma. The defect extended from just below the nipple almost to the umbilicus, and measured 28 x 30 cm. An "extended" latissimus dorsi muscle flap and extended deep inferior epigastric artery flap were used for reconstruction of the defect. A 1-year follow-up of the patient is presented.

Abdominal Neoplasms↗
PubMed1992

Effect of fertility regulating agents on motility and zona-free hamster egg penetration by spermatozoa of bonnet monkey.

Administration of STS-557 (17 alpha-cyanomethyl-17 beta-hydroxyestra 4,9(10)-dien-3-one; 12 mg/monkey daily) for 4 weeks either alone or in combination with 20 Aet-1 (testosterone-trans-4-n-butyl cyclohexyl carboxylate; code CDB 1781; 40 mg/monkey single administration) had no significant effect on motility and zona free hamster egg penetration by spermatozoa of bonnet monkey, but continuation of the treatment for 12 weeks reduced (in one monkey treated with STS-557) or abolished (one treated with STS-557 and two with STS-557 + 20 Aet-1) the motility as well as zona-free hamster egg penetration (by spermatozoa of all treated monkeys). Motility and the ability to penetrate zona-free hamster egg returned to normalcy after 10 weeks of withdrawal of treatments. Active immunization of monkeys with ovine FSH (4 weeks after booster) had no adverse effect on motility of spermatozoa but none of the zona-free hamster eggs was fertilized. The correlation between motility and the capacity to penetrate the zona-free hamster eggs by monkey spermatozoa varies with the treatment. Such correlation was apparent in monkeys treated with STS-557 but not in monkeys immunized with ovine FSH.

Animals↗
PubMed1992

Use of sedation analgesia for pediatric dentistry.

26 healthy children between the ages of 36 and 60 months (mean 35 months) who satisfied the selection criteria during a screening visit participated in this double blind study. The subjects were assigned randomly to receive either 75 mg/kg Triclofos elixir (Regimen I-21 children) or 50 mg/1kg Trichlofos elixir combined with 1 mg/kg promethazine elixir (Regimen II-22 children). All medications were given orally 45 minutes before treatment. During operative procedures all subjects received nitrous oxide/oxygen at a concentration of 35%. All the patients were restrained in a papoose board (Indigenous). The subjects were monitored for vital signs and evaluated for sedation and sleep, movement, crying and overall behaviour before, during and after the operative procedure. Regimen II was found to be superior to Regimen I with regard to behaviour management of difficult young children. However extremely apprehensive children were not good subjects for this sedation technique.

Anesthesia, Dental↗
PubMed1992

[The mechanism of inhibition of calmodulin-dependent cyclic nucleotide phosphodiesterase by dihydropyridine calcium antagonists].

Kinetic studies of the monoclonal antibody-purified 60 kd calmodulin dependent cyclic nucleotide phosphodiesterase (PDE) from bovine brain indicate that the dihydropyridine calcium antagonists, nicardipine and felodipine are partially competitive inhibitors of the enzyme. This was supported by the facts that the inhibition approached a finite level as the concentrations of drug reached saturation and the inhibition showed non-linearity characteristics in the Dixon plot. Furthermore, at the constant concentration of felodipine which brings about close to maximal inhibition, increasing concentrations of nicardipine can alleviate enzyme inhibition to approach the level of maximal nicardipine inhibition, suggesting that the calmodulin-dependent PDE may contain specific dihydropyridine binding site distinct from the active site.

Binding, Competitive↗