Estimate of methane emissions from the U.S. natural gas industry.

Global methane emissions from the fossil fuel industries have been poorly quantified and, in many cases, emissions are not well-known even at the country level. Historically, methane emissions from the U.S. gas industry have been based on sparse data, incorrect assumptions, or both. As a result, the estimate of the contribution these emissions make to the global methane inventory could be inaccurate. For this reason the assertion that global warming could be reduced by replacing coal and oil fuels with natural gas could not be defended. A recently completed, multi year study conducted by the U.S. Environmental Protection Agency's Office of Research and Development and the Gas Research Institute had the objective of determining methane emissions from the U.S. gas industry with an accuracy of +/-0.5% of production. The study concluded that, in the 1992 base year, methane emissions from the industry were 314 +/- 105 Bscf or 6.04 +/- 2.01 Tg (all conversions to international units are made at 15.56 degrees C and 101.325 kPa).

Biomolecular absorption of ultrasound: II. Molecular structure.

Measurements of absorption coefficients in several globular and linear proteins yield no correlations of absorption with alpha-helix content or with the number of polypeptide chains in the protein. Removal of all but the primary structure with denaturing agents that convert proteins to random chains causes only small changes in the absorption of globular proteins. Complete denaturing of linear muscle proteins results in large reductions in absorption. Therefore, it is concluded that absorption in globular proteins is insensitive to structural characteristics while in linear proteins it is dependent upon the amount of alpha-helix content. An alternative explanation of the results is that alpha-helix contributes to absorption in both globular and linear proteins but tertiary structure in globular proteins reduces absorption because of inhibited solvent interactions.

Biomolecular absorption of ultrasound. I: Molecular weight.

Amino acid solutions have absorptions which are generally small compared to those for proteins. Proteolytic enzyme treatment of proteins in solution reduces their absorption. These observations suggest that absorption increases with molecular weight. However, measurements of sugars, polysaccharides, amino acids, and proteins yield no correlations of absorption with molecular weight within these groups. Therefore, it is concluded that absorption increases in these molecules with increasing molecular weight only in a threshold sense, with absorption increasing significantly only in a restricted molecular weight range. This range may approximate that observed for polyethylene glycol and dextran, viz., 1 to 100 monomer units. However, there is some indication that the transition range may be narrower than a factor of 100 in molecular weight.

Peritoneal encapsulation and abdominal cocoon. Case reports and a review of the literature.

Peritoneal encapsulation and abdominal cocoon are rare entities, with only 7 and 13 cases, respectively, having so far been reported. A case of each of these conditions is emphasized. Peritoneal encapsulation is probably a development abnormality, largely asymptomatic, and found incidentally at laparotomy or autopsy. The accessory membrane present in front of the small bowel can be easily removed, but excision may not be necessary. Abdominal cocoon is a total or partial encapsulation of the small bowel. It has a tropical or subtropical distribution and presents in young girls as acute or chronic bowel obstruction. Complete recovery is the rule after removal of the membrane. The first example of preoperative radiologic diagnosis is presented. An infective etiology is suggested.

Fluorescence of buried tyrosine residues in proteins.

Histone H1 contains only one tyrosine and no tryptophan. The intrinsic fluorescence of the tyrosine rises by about 400% as the protein folds from a random coil to a globular structure (Giancotti, V., Fonda, M. and Crane-Robinson, C. (1977) Biophys. Chem. 6, 379-383). Measurements of external quenching by a large variety of quenchers shows very much reduced quenching in the folded state as compared to the disordered. It is concluded that the tyrosine is a buried residue. This is supported by the observation that the fluorescence of modified amino-tyrosyl H1 is similar to that of buried tyrosines in ribonuclease. The classification of tyrosine fluorescence in tryptophan-free proteins (Cowgill, R.W. (1976) in Biochemical Fluorescence Concepts, Vol. 2 to include the case of residues buried in a hydrophobic environment and having a relative quantum yield RTyr, greater than unity.

Extensive carboxypeptidase digestion of clam alpha-paramyosin. The effect on the size and solubility of the residual protein.

The purpose of this paper is to provide further evidence that the C-terminal 1/3 of the alpha-paramyosin molecule is the portion responsible for the low solubility of alpha-paramyosin at neutral pH and low ionic strength. This was accomplished by digesting from the C-terminal end with carboxypeptidases A and B in 2 M urea at pH 8.5. The solubility increased as the molecular weight decreased until a stable segment 2/3 of the size of the molecule remained.

Structural difference between alpha-paramyosin and beta-paramyosin of Mercenaria mercenaria.

A method is described for extraction of alpha-paramyosin in amounts comparable to that formerly attained for beta-paramyosin (15-25 mg/g of muscle). A modification of the procedure for sodium dodecyl sulfate gel electrophoresis is described that permits the separation on coelectrophoresis of alpha-paramyosin (207 000 daltons) and beta-paramyosin (200 000 daltons). The alpha- and beta-paramyosins also can be distinguished by gel electrophoresis at pH 2.3 and by differences in solubility in the region of 0.2-0.4 ionic strength at neutral pH. Evidence is presented that the segment lost from alpha-paramyosin during degradation to beta-paramyosin came from the C-terminal end. This evidence is based on determinations of N- and C-terminal amino acids and on the size of segments obtained after chemical cleavage at the sites of Cys residues. It has been observed earlier that the solubility characteristics of beta-paramyosin at neutral pH are determined by the C-terminal one-third of the molecule and the present results indicate that the additional small segment of about 3.5% of the total mass that is present in the C-terminal end of alpha-paramyosin accounts for the marked difference in solubility of the two forms.

Fluorescence and the structure of proteins. XXI. Fluorescence of aminotyrosyl residues in peptides and helical proteins.

1. Five peptides containing tyrosine were converted to the 3-aminotyrosyl peptides by nitration with tetranitromethane and subseuqent reduction of the nitro groups to amino groups. The fluorescence of these aminotyrosyl residues was found to be quite similar to that of 3-aminotyrosine and it is concluded that the fluorescence is not sensitive to incorporation of the amino acid into the peptide chain. 2. Fluorescence of 3-aminotyrosine derivatives was sensitive, however, to the nature of the solvent; as the dielectric constant decreased, fluorescence was enhanced ten fold and the emission maximum shifted from the 350-370 nm value in aqueous solution to 320 nm. It is predicted that similar differences might be expected for exposed and buried aminotyrosyl residues in a protein. 3. Exposed tyrosyl residues on the helical protein tropomyosin and a helical segment of paramyosin were aminated in part (39% and 34% of the total tyrosyl residues, respectively). The fluorescence of the aminated tyrosyl residues on these proteins was similar to that of the aminotyrosyl peptides in an aqueous medium. Although the fluorescence efficiency of an aminotyrosyl residue was much lower than that of a tyrosyl residue, it was easy to distinguish the fluorescence of the aminotyrosyl residues (350-355 nm) on the protein from that arising from unmodified tyrosyl residues (305 nm).

Fluorescence and the structure of proteins. XXII. Fluorescence of aminotyrosyl residues formed in ribonuclease A.

1. Tyrosyl residues on ribonuclease A were nitrated with tetranitromethane and then reduced to aminotyrosyl residues. By variation of reaction conditions and degree of exposure of tyrosyl residues it was possible to convert from 1 to all 6 tyrosyl to aminotyrosyl residues. 2. At the lower levels of 1-3 aminated tyrosyl residues/molecule the change in conformation seemed minor and 70% of the enzymatic activity was retained. When the three buried tyrosyl residues or all six residues were aminated only 5% of the enzymatic activity was retained. 3. Titration data, susceptibility to urea denaturation, and fluorescence characteristics indicated that some of the aminotyrosyl residues were buried in the interior and others were exposed on the surface of the protein. On the basis of the activation/emission wavelengths it was possible to distinguish buried (288/320 nm) and exposed (288/365-395 nm) aminotyrosyl residues as well as exposed tyrosyl residues (275-305 nm). 4. The modification of specific tyrosyl residues on a protein to aminotyrosyl residues appears to have some promise for observation of changes in environment of the residues that accompany various conformation changes by monitoring the fluorescence.

The structure and stability of trypsin-resistant segments from rabbit tropomyosin.

Tropomyosin was found to undergo only limited digestion by trypsin at 0 degrees C and the two segments that accumulated amounted to two-thirds of the original protein. They are referred to as segments A and B. These segments were not resistant to trypsin digestion at 20 degrees C and at the latter temperature no large fragments remained as judged by disc gel electrophoresis. Segments A and B were separated from each other on the basis of solubility differences and were found to have molecular weights of 24600 and 21900 respectively. Each of the segments appeared to retain about 70-75% of the helical conformation as judged by circular dichroism at 20 degrees C. However, the segments did not show any of the inhibitory activity of the parent tropomyosin molecule when mixed with troponin in the Mg2+-actomyosin ATPase system. Amino acid analysis showed that the portion of tropomyosin that was digested by trypsin (EC 3.4.21.4) had a lower content of the helix stabilizing residues Glu and Leu and a higher content of the helix-destabilizing residues Arg and Lys. These differences indicate that the digested portion should be less stable in the helical conformation than the two trypsin-resistant segments. End group determinations along with the results of the amino acid analysis indicated that segment A was probably derived from the central one-third of tropomyosin and segment B from the C-terminal one-third. By the process of elimination the N-terminal third appears to have been more liable region that was digested by trypsin. The segments A and B were shown to differ in their stability to denaturation by guanidine-HCl and elevated temperature. All of these observations indicate that tropomyosin is not a uniform structure and is composed of regions of different stability.

Segments of paramyosin formed by cleavage at sites of cysteine residues.

The helical muscle protein beta-paramyosin of 200,000 was treated by the general method of G. R. Jacobson et al. (1973), J. Biol. Chem. 248, 6583) for cleavage of the polypeptide chain at the site of Cys residues. The protein cleaved into two segments: CCF-1 of 140,000 daltons and CCF-2 of 60,000 daltons. The two segments were separated and some properties were compared. Circular dichroism measurements indicated that CCF-1 was completely helical and that CCF-2 was 85% in the alpha-helical form. The molecular size, resistance to pepsin digestion, stability to heat and urea, and solubility of CCF-1 were all similar to corresponding properties of a pepsin-resistant segment PPC-1 described earlier (Cowgill, R. W. (1972), Biochemistry 11, 4532). By contrast, the properties of CCF-2 were distinctly different. It was concluded that the CCF-1 segment, like the PPC-1 segment, arose from the N-terminal two-thirds of the paramyosin molecule. The CCF-2 segment from the C-terminal one-third of paramyosin had limited solubility at neutral pH that matched the low solubility of paramyosin. It was concluded that the CCF-2 region is responsible for the self-aggregating tendency of paramyosin at neutral pH and low ionic strength.

Proteolysis of paramyosin from Mercenaria mercenaria and properties of its most stable segment.

The helical muscle protein paramyosin appears to consist of three segments of approximately equal size that differ in stability to guanidine hydrochloride and heat. The N-terminal segment is most stable and the C-terminal segment is least stable. These differences in stability serve as a basis for design of proteolytic digestions to specifically remove segments of low and intermediate stability. Thus, at room temperature only the C-terminal region was susceptible to digestion by pepsin or trypsin. Proteolytic removal of the latter region resulted in the accumulation of the remaining two-thirds of the paramyosin molecule as a segment (PPC-1) of 140,000 daltons that was still in a stable helical conformation. Proceeding to more rigorous conditions, papain digestion of either paramyosin or PPC-1 in 4 M guanidine-HCl that would be expected to destabilize all but the N-terminal segment did result in cleavage of all except that region. The N-terminal region accumulated as a helical segment of 74,000 daltons (PPC-2) if digestion was limited to 1.5 hr or a smaller segment of 58,000 daltons (PPC-3) if digestion continued for 24 hr. Stability of the three PPC segments to guanidine-HCl and heat was measured by change in fluorescence of tyrosyl residues upon loss of the helical conformation. The stability of the segments corresponded well with the stability of those regions in the paramyosin molecule from which the segments were believed to have come. Amino acid composition of the PPC segments and of paramyosin were all very similar, and prediction of relative stability of these helical proteins from inspection of gross amino acid composition does not appear promising.