Search PubMed⌕ Search

Biomedical subjects

M Levine

Publications and source records attributed to M Levine.

At least 541 records · Page 30Linked to original sources
PubMed1976

A comparative study of the glycolipids of human, bird and fish testes and of human sperm.

The glycolipids of human testis and sperm have been compared. Both adult testis and the sperm exhibited remarkably complex, but generally similar, patterns of glycolipids. In particular, both contained appreciable amounts of the sulfogalactosylmonoalkylmonoacylglycerol, recently shown to be the principal glycolipid of the testis and sperm of a number of animals. In contrast, immature (prebuteral) human testis did not contain this compound. To extend knowledge on the possible distribution of sulfogalactosylmonoalkylmonoacylglycerol in the testes of other chordates, we have also analysed the glycolipids of the testes of a number of birds and fish. None of the testes from these species contained the above compound. Instead, sulfogalactosylceramide was found to be a major glycolipid of the testis of mature fowl, duck and skate-fish and sulfogalactosylglucosylceramide of the testis of mature salmon and trout. Immature duck testis contained only a trace of sulfogalactosylceramide. These studies reveal intriguing differences between the sulfatides of various chordates, lend support to the concept that sulfatides increase markedly in testis at a specific stage of spermatogenesis and suggest an important role for sulfatides in testicular and spermatozoal function.

Adult↗
PubMed1976

Urea-extractable protein from human epidermis.

The major protein fraction extracted from human epidermis by urea has the following characteristics: (1) A molecular weight of approximately 600 000. (2) A copper content of 0.03% giving a minimum molecular weight of 212 000. (3) A non-protein moiety indicated by (a) protein/dry weight ratio (b) anomalous ultraviolet absorption spectrum (c) high-voltage electrophoresis after mild alkaline or acid treatment (d) an excess of imidazole groups by Pauly reaction compared with the number of histidine residues by amino acid analysis. The non-protein component is not urocanic acid or RNA as has been reported (Bernstein, I.A. (1970), J. Soc. Cosmet, Chem. 21, 583-594 and Sibrack, L. A., Gray, R. H. and Bernstein, I. A. (1974), J. Invest. Dermatol. 62, 394-405). (4) The presence of interchain disulphide linkages indicated by polyacrylamide gel electrophoresis in sodium dodecyl sulphate with and without beta-mercaptoethanol. (5) Polyacrylamide gel electrophoresis in presence and absence of 6 M urea suggests that aggregates are broken down in urea.

Amino Acids↗
PubMed1976

The biochemistry of the renin-angiotensin system and its role in hypertension.

The renin-angiotensin system has an important role in maintaining elevated blood pressure levels in certain forms of experimental and human hypertension. Renin, an enzyme produced by the juxtaglomerular cells of the kidney, acts on a protein substrate found in the alpha 2-globulin fraction of the plasma to produce a decapeptide, angiotensin I. This decapeptide is not directly pressor, but on passage through the pulmonary circulation is converted to an octapeptide, angiotensin II, a very potent pressor substance which acts by causing constriction of arteriolar smooth muscle. In addition to its direct action which increases blood pressure, angiotensin II acts on the adrenal cortex to cause the release of the sodium-retaining hormone aldosterone. Recent evidence suggests that this action may be mediated by the heptapeptide, angiotensin III. Both renin and its protein substrate exist in multiple forms and renin may also exist as a high molecular-weight "pro-hormone," although the physiologic significance of these forms is not clear. The elucidation of the biochemistry of the renin-angiotensin system has provided us with inhibitors which allow the system to be blocked effectively in vivo. Thus, angiotensin antagonists such as Sar 1, IIe 8-angiotensin II and converting enzyme inhibitors such as BPP 9a (SQ 20881) have proved useful in the study of experimental and human hypertension.

Aldosterone↗
PubMed1976

Kinetic properties of pulmonary angiotensin-converting enzyme. Hydrolysis of hippurylglycylglycine.

Some of the kinetic properties of angiotensin-converting enzyme (peptidyl-dipeptide hydrolase, EC 3.4.15.1) purified from hog lung have been determined using hippurylglycylglycine as substrate. The effects of pH and ionic environment on enzyme activity are complex and interdependent. At 0.1 M NaCl, the pH-activity curve shows an abrupt decrease in V/Km as the pH rises from 6 to 6.5, implying that ionization of a group in the enzyme with a pK in this range aids in binding of the substrate. Chloride is required for enzyme activity; there are two phases in the effect of NaCl. At both pH 6 AND 8, THE FIRST PHASE (UP TO 0.1 M NaCl) is activation. The second phase (above 0.1 M) at pH 6 is inhibition, while at pH 8 there is further activation which appears to be dependent upon ionic strength rather than a specific Cl-effect. Activation by cobalt and inhibition by EDTA are somewhat more effective at pH 6 than at pH 8. The nonapeptide inhibitor less than Glu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro is nearly equipotent at both pH 6 and 8, but Arg-Pro-Pro is more inhibitory at pH 8 than at pH 6.

Animals↗
PubMed1976

Effect of dimethyl sulfoxide on permeability of human skin in vitro.

A diffusion flow cell is described for the continuous monitoring of skin permeability. The technique was used to study the permeability behavior of human skin subsequent to treatment with dimethyl sulfoxide. Such treatment produced an increased penetration rate of tritiated water, which was dependent upon the time of exposure and the concentration of dimethyl sulfoxide applied. Removal of the solvent resulted in partial recovery of barrier capacity. Skin, incubated in vitro in growth medium containing dimethyl sulfoxide, survived only at very low concentrations. Degeneration occurred after a few days in 4.5% dimethyl sulfoxide and much sooner at higher concentrations.

Autoradiography↗
PubMed1976

Partial purification of a high molecular weight renin from hog kidney.

Previous investigators have reported finding a high molecular weight (HMW) renin in various species which is activated by acidification. Two laboratories have reported that a decrease in molecular weight of the renin accompanies the acidification step. This report describes the partial purification of an HMW renin from hog kidney extracts which had previously been acidified to pH 2.5. The HMW renin, with a molecular weight of 57,000-59,000, constitutes only a small, relatively constant fraction of the total renin isolated. Omission of the acidification step or initial acidification to pH 1.6 does not change the amount of HMW renin significantly. The HMW renin attacks the protein substrate to produce angiotensin at about one-fourth the rate expected, based upon the rate at which it cleaves the tetradecapeptide substrate or a model nonapeptide substrate. It is inactivated by antiserum to hog kidney renin prepared in dogs. It is less stable than hog renin when stored at 0 degrees C. The HMW renin has a pH optimum between 6.5 and 7.0. It is not activated by acidification to pH 3, nor by tryptic or peptic digestion. We have been unable to activate HMW renin or to change its molecular weight by procedures reported by other investigators and therefore conclude that the HMW renin differs from material previously reported and may be an isoenzyme of renin.

Angiotensin II↗
PubMed1976

Chronic one-kidney hypertension in rabbits. II. Evidence for a new factor.

The arterial pressure of rabbits with chronic one-kidney hypertension can be lowered to normotensive levels by direct immunization with preparations made from the cortex of hog kidneys. Hypertensive rabbits that are immunized with large amounts of renin may develop high plasma antirenin titers without affecting their blood pressure. Removal of renin by chromatography on columns of immobilized antirenin yields preparations with little or no renin. Such preparations may be effective in lowering blood pressure although they do not elicit the formation of plasma antirenin and the rabbits remain sensitive to challenging doses of rabbit renin. The evidence suggests that an unknown substance is responsible for the development of a cross-reacting antibody that neutralizes an unknown factor that is essential for the maintence of an elevated blood pressure level in rabbits with chronic one-kidney hypertension.

Animals↗
PubMed1975

Bacteriophage P22 virion protein which performs an essential early function. I. Analysis of 16-ts mutants.

The product of gene 16 of phage P22, P16, is a head protein. P16 does not play an essential role in phage assembly since particles formed without this protein appear normal by electron microscopy examination (Botstein et al., 1973). P16 is essential when the particle infects a cell in the following cycle of infection (Botstein et al., 1973; King et al., 1973). We have characterized a mutant of P22 carrying a temperature-sensitive allele of gene 16. This mutant has previously been referred to as P22 25-ts (Levine et al., 1970, 1972) and P22 X-ts (Bezdek and Soska, 1970, 1973). P22 16-ts behaves as an early mutant at the nonpermissive temperature. Temperature shift experiments show that P16 of the infecting virion acts within the first 10 min at 25 C and that gene 16 product is required late in the latent period for incorporation into infectious phage. Induction does not require P16 for the production of particles. Particles produced either in a P22 16-ts thermal shift-up infection or after induction of 16-ts lysogens at 41 C are missing P16 and are, therefore, defective. P16 in P22 16-ts virions formed at the permissive temperature appears to be heat labile; it is inactivated after infection at 41 C. A simple assay for defective particles based on a complementation test is described.

DNA, Viral↗
PubMed1975

Bacteriophage P22 virion protein which performs an essential early function. II. Characterization of the gene 16 function.

P16 is a virion protein and, as such, is incorporated into the phage head as a step in morphogenesis. The role of P16 in assembly is not essential since particles are formed without this protein which appear normal by electron microscopy. P16 is essential when the particle infects a cell in the following cycle of infection. In the absence of functional P16, the infection does not appear to proceed beyond release of phage DNA from the capsid. No known genes are expressed, no DNA is transcribed, and the host cell survives the infection, continuing to grow and divide normally. The P16 function is required only during infection for the expression of phage functions. Induction in the absence of P16 proceeds with the expression of early and late genes and results in particle formation. P16 must be incorporated during morphogenesis into progeny particles after both infection and induction for the progeny to be infectious. The P16 function is necessary for transduction as well as for infection. Its activity is independent of new protein synthesis and it is not under immunity control. P16 can act in trans, but appears to act preferentially on the phage or phage DNA with which it is packaged. The data from complementation studies are compatible with P16 release from the capsid with the phage DNA. In the absence of P16 the infection is blocked, but the phage genome is not degraded. The various roles which have been ruled out for P16 are: (i) an early regulatory function, (ii) an enzymatic activity necessary for phage production, (iii) protection of phage DNA from host degradation enzymes, (iv) any generalized alteration of the host cell, (v) binding parental DNA to the replication complex, and (vi) any direct involvement in the replication of P22 DNA. P16 can be responsible for: (i) complete release of the DNA and disengagement from the capsid, (ii) bringing the released DNA to some necessary cell site or compartment such as the cytoplasm, (iii) removal of other virion proteins from the injected DNA, and (iv) alterations of the structure of the injected DNA.

Adsorption↗
PubMed1975

Isolation and partial characterization of a sulfogalactoglycerolipid from rat brain.

The brain of adult rats were analyzed for the presence of 35-SO4-containing glycolipids following intraventricular injection of Na2-35SO4. Radiochromatographic analyses revealed the presence of two minor 35-SO4-containing glycolipids, in addition to sulfogalactosylceramide. One of these two minor sulfolipids was isolated and tentatively identified as a 1-O--alkyl-2-0-acyl-3-(3'-sulfogalactosyl)-glycerol, a compound recently demonstrated to be the major glycolipid of mammalian testis. The alkyl and acyl compositions of the compound from rat brain are more heterogeneous than those from rat testis. The non-sulfated form of the galactoglycerolipid was also detected in rat brain. The amount of the sulfogalactoglycerolipid in rat brain is 0.19 mumol per gram wet weight, approximately one-third of the amount in rat testis (per gram wet weight), and is approximately one-fifteenth that of sulfogalactosylceramide in rat brain. The possible significance of the common occurrence in brain and testis of sulfated and non-sulfated galactolipids is discussed.

Animals↗
PubMed1975

Chronic one-kidney hypertension in rabbits. I. Treatment with kidney extracts.

An investigation into the mechanism that sustains the blood pressure in chronic one-kidney hypertension in rabbits was made using passive and active immunization with hog kidney extracts containing renin and with angiotensin antagonists. Seven hypertensive rabbits were passively immunized for extended periods with antiserum prepared in other rabbits. Antirenin levels were in the range of 1-3 units/ml. Control experiments demonstrated that antirenin concentrations of 1.0 unit/ml or more eliminated more than 99% of the pressor response to renin. There was no lowering of blood pressure that could be attributed to the antibodies. No decrease in blood pressure was observed in 13 experiments in 7 rabbits given the angiotensin II antagonist 1-Sar-8-Ile-angiotensin II; infusion rates of 0.09-87 mug/min kg-1 were used for periods of a few hours up to 3 days. A reduction in blood pressure occurred in 16 of 19 rabbits immunized directly with extracts containing renin with specific activities of 9.6-757 GU/mg. Plasma antirenin titers correlated poorly with reductions in blood pressure. The blood pressure of 22 rabbits given equal amounts of protein without renin was unaffected. It is concluded that the elevation of blood pressure in rabbits with chronic one-kidney hypertension is not dependent on ciculating renin or angiotensin; rather, it results from the presence of renin in an extravascular location or from an unknown pressor substance.

Angiotensin II↗