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Biomedical subjects

M L Green

Publications and source records attributed to M L Green.

71 records · Page 4Linked to original sources
PubMed1977

Biochemical catalysis involving coenzyme B-12: a rational stepwise mechanistic interpretation of vicinal interchange rearrangements.

A mechanism is proposed for the catalytic action of coenzyme B-12 which is consistent with current knowledge of organometallic reactions and with the experimental data now available from biochemical studies. A key feature of the proposal is an electrocyclic cleavage of the coenzyme that reduces cobalt and also leads to a 1,19-seco-corrin. The seco-corrin serves as a tridentate ligand about Co(I). This arrangement permits the metal to take part in the kinds of organometallic reactions that are ideal for coenzyme B-12 catalysis, including oxidative addition and its reverse, reductive elimination. It is further proposed that the rearrangement steps involve cobaltcarbene complexes.

Catalysis↗
PubMed1977

Calcium hydroxide and potassium nitrate as desensitizing agents for hypersensitive root surfaces.

The purpose of this investigation was to evaluate calcium hydroxide and potassium nitrate individually as densensitizing agents for hypersensitive root surfaces. The apparatus used in the experiment to measure hypersensitivity was (a) a thermo-electric stimulating device to measure hot and cold stimulation quantitatively and (b) a mechanical stimulating device to measure scratch stimulation quantitatively. The conclusions drawn from the study were: 1. Calcium hydroxide was more consistently effective in decreasing sensitivity then was potassium nitrate or the control. 2. Calcium hydroxide as compared to the control was statistically (99% level of significance) more effective in reducing sensitivity to mechanical, hot and cold stimulation immediately and at the conclusion of the experiment (3 months). 3. It appears that calcium hydroxide could be used as a desensitizing agent initially following periodontal surgery to reduce pain from hypersensitive roots in order that proper oral hygiene could be reestablished.

Adult↗
PubMed1975

The effect of acid proteinase inhibitors on chicken pepsin.

1. The activity of chicken pepsin was partially inhibited by dimethyl-(2-hydroxy-5-nitrobenzyl)sulphonium bromide, but was unaffected by p-bromophenacyl bromide. 2. In the presence of Cu2+, diazoacetylnorleucine methyl ester completely inactivated chicken pepsin with the incorporation of 1 mol/mol. The mechanism of the reaction was similar to that with pig pepsin. 3. Chicken pepsin was completely inactivated by 2-diazo-4-bromoacetophenone in the presence of Cu2+. 4. Chicken pepsin was almost completely inactivated by 1,2-epoxy-3-(p-nitrophenoxy)propane at 25 degrees C, 3-4mol of inhibitor/mol being incorporated. The reaction at 10 degrees C was investigated briefly. 5. Calf chymosin was inactivated by 1,2-epoxy-3-(p-nitrophenoxy)propane at 10 degrees C, the incorporation of 1 mol/mol being required for complete inhibition. 6. The characteristics of the reactions of chicken pepsin with the above compounds were compared with those of other acid proteinases.

Acetophenones↗
PubMed1975

Crystallization of one of the chicken pepinogens and its derived pepsin.

Dodecahedral crystals of chicken pepsinogen have been prepared, one perfect cystal having the dimensions 0.090mm x 0.086mm x 0.009mm. The derived pepsin crystakkized in the form of flat plates, often with one rounded end. The dimensions of one such crystal wer 0.076mm x 0.043mm. Both types of protein crystals showed full enzymic or potential enzymic activity.

Crystallization↗
PubMed1973

The purification and properties of a single chicken pepsinogen fraction and the pepsin derived from it.

1. Evidence is given for the presence of at least five pepsinogens in a crude extract of mixed chicken stomachs. One of these was purified and could be activated to yield a single pepsin. 2. The molecular weights of the pepsinogen and pepsin were 36000 and 34000 respectively. The pepsin associated at low pH values and low ionic strength. 3. The amino acid analyses of both proteins are given. The pepsin was devoid of phosphate but contained carbohydrate. 4. The N-terminal amino acids of pepsinogen and pepsin were serine and threonine respectively. Five amino acids were released by carboxypeptidase A and it was deduced that serine may be the C-terminal one. 5. Each protein contained one thiol group per molecule as determined by titration with p-chloromercuribenzoate. The rate of the reaction was very rapid with pepsin, but much slower with pepsinogen, although the same group appeared to react in both instances. The enzymic activity of pepsin was unaffected by the modification. 6. The isoionic point of the pepsin was close to pH4.0 and the enzyme was stable for long periods at pH values up to 7.0. 7. The enzyme hydrolysed bisphenyl sulphite almost as rapidly as did pig pepsin A.

Amino Acids↗
PubMed1969

Studies on the preparation of water-insoluble derivatives of rennin and chymotrypsin and their use in the hydrolysis of casein and the clotting of milk.

1. Enzymically active insoluble derivatives of chymotrypsin and rennin were prepared by coupling each enzyme to agarose as described by Porath, Axén & Ernback (1967) and rennin to aminoethylcellulose by the method of Habeeb (1967). 2. Agarose-chymotrypsin was stable over the range pH2-9, but agarose-rennin released active enzyme into solution at above pH2 and aminoethylcellulose-rennin was similarly unstable at certain pH values. 3. Each derivative appeared to catalyse the clotting of milk at 30 degrees , but this was probably entirely due to enzyme released into solution from the carrier. 4. The presence of a competitive inhibitor of chymotrypsin during its coupling to agarose had no effect on the activity or stability of the resulting derivative. 5. The characteristics of agarose and cellulose render them not entirely suitable for use in a continuous system with milk.

Animals↗
PubMed1969

Cation-activated nucleotidase in cell envelopes of a marine bacterium.

Isolated cell envelopes of a marine bacterium, M.B.3, have been prepared which possess a nonspecific, cation-activated nucleotidase. The cell envelope comprises approximately 35% (dry weight) of the whole cell and contains protein, 60.2%; lipids, 20.7%; hexose, 3.4%; and ribonucleic acid, 4.6%. No deoxyribonucleic acid could be detected in the preparations. The nucleotidase has an essential requirement for Mg(2+); maximum activation at pH 8.0 occurs at a divalent cation concentration of approximately 80 mm. At a Mg(2+) to adenosine 5'-triphosphate (ATP) ratio of 2:1, the enzyme was further stimulated by monovalent cations Na(+), K(+), NH(4) (+), and Li(+). Maximum activity was found at a monovalent ion concentration of approximately 0.3 m. The envelope preparation liberated inorganic orthophosphate (P(i)) from ATP, adenosine 5'-diphosphate (ADP), and adenosine 5'-monophosphate (AMP) at similar rates. Thin-layer and ion-exchange chromatography show that when AMP, ADP, and ATP were utilized as substrate, approximately 1, 2, and 3 moles of P(i), respectively, were produced per mole of adenosine. P(i) was also liberated from the 5'-triphosphates of guanosine, uridine, and cytidine. The enzyme preparation did not attack p-nitrophenyl phosphate, beta-glycerophosphate, or inorganic pyrophosphate. Sulfhydryl inhibitors p-chloromercuribenzoate, N-ethyl maleimide, and iodoacetate had little effect upon the nucleotidase activity. Ca(2+) and ethylenediaminetetraacetic acid caused complete inhibition of the system, whereas ouabain had no effect upon the enzyme activity. The concentrations of Na(+) (0.3 m) and Mg(2+) ions (60 to 80 mm) required for maximum ATP-hydrolyzing activity were similar to those concentrations necessary for maintenance of cell integrity and for the prevention of cell lysis.

Adenine Nucleotides↗
PubMed1968

The oxidation of aminoacetone by a species of Arthrobacter.

1. A micro-organism similar to Arthrobacter globiformis has been isolated from sewage by elective growth on a medium containing l-threonine as sole source of carbon and nitrogen. 2. Washed cell suspensions of the organism catalyse the complete disappearance of aminoacetone from the medium and its almost complete oxidation. 3. In the presence of iodoacetate, aminoacetone disappearance is accompanied by the accumulation of methylglyoxal, about 70% of the aminoacetone removed being accounted for in this way. 4. It is suggested that the conversion of aminoacetone into methylglyoxal is catalysed by an amine oxidase.

Acetone↗
PubMedDate not supplied

Is experience a good teacher? How interns and attending physicians understand patients' choices for end-of-life care. SUPPORT Investigators. Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments.

BACKGROUND: Recent studies have shown that physicians do not accurately assess patients' health status or treatment preferences. Little is known, however, about how physicians' levels of training or experience relate to their abilities to assess these preferences. To better understand this phenomenon, the authors compared the abilities of medical interns and attending physicians to predict the choices of their adult patients for end-of-life care. METHODS: 230 seriously-ill adult inpatients were surveyed about their desires for cardiopulmonary resuscitation, their current quality of life, and their attitudes toward six other common adverse outcomes. The medical intern and attending physician who cared for these patients were asked to estimate the patient's responses for all of the same items. Agreement was assessed using the kappa statistic. RESULTS: Compared with interns, attending physicians had known patients longer, had talked with patients more frequently about prognosis, and felt they knew more about their patients' preferences (all p < .0001). Despite this, the attending physicians were no more accurate than the interns in assessing patients' preferences. Both interns and attending physicians had only a fair understanding of patients' preferences for cardiopulmonary resuscitation or their quality of life (kappa statistics 0.32 to 0.47), and even less understanding of their willingness to tolerate adverse outcomes (kappa statistics -0.03 to 0.37). CONCLUSIONS: For this cohort of seriously ill patients, neither medical interns nor their attending physicians were consistently accurate in assessing patients' preferences, and attending physicians were not more accurate than medical interns. Attending physicians should not assume that they can infer patients' preferences any better than the interns caring for these hospitalized patients.

Adult↗