1H nuclear magnetic resonance study of the prosthetic group in sulfhemoglobin.

The molecular and electronic structure of the modified prosthetic group of sulfhemoglobin (SHb) was investigated by 1H NMR for the low-spin ferric cyano-met and high-spin ferrous deoxy sulfhemoglobin complex. The 1H NMR resonances of the two subunits in the cyano-met SHb complex were differentiated on the basis of the differential stability toward regeneration of native subunits. The subunit origin for the two sets of resonances was established by formation of the sulfglobin protein for the isolated alpha-chain prior to assembling with the native beta-subunit to yield a tetramer with sulfhemin in the alpha-subunits. The subunit peak assignments establish that it is the beta-subunit of SHb which regenerates more rapidly to native protein. The hyperfine shifted sulfhemin peaks were assigned based on steady-state nuclear Overhauser effects which demonstrated that similarly hyperfine shifted peaks exhibit the same dipolar connectivities observed in the analogous sulfmyoglobin complex. Hence it is concluded that pyrrole B is the site of reaction in both hemoglobin and myoglobin. The initially formed SHb complex failed to equilibrate to yield a complex with a sulfhemin sufficiently stable to extraction as found previously for sulfmyoglobin. However, apoHb readily bound the green sulfhemin extracted from the terminal alkaline equilibration product of sulfmyoglobin. The inhibition on the equilibration to the alkaline form with the exocyclic thiolene ring is attributed to the interaction with Val FG5. The observations of the same dipolar connectivities among similarly hyperfine shifted peaks in the directly prepared and reconstituted SHb complexes further support the same structure for the sulfhemin in sulfmyoglobin and SHb. The strongly hyperfine shifted peaks in the deoxy form of both SHb complexes were found very similar to those of the analogous sulfmyoglobin complexes. The proximal His labile ring proton signal appears to experience a 5- to 10-ppm decrease upon conversion of a native globin to sulfglobin. This attenuation may provide a probe for differentiating chlorins and hemins in globin pockets.     

Molecular basis for the polymorphic forms of human serum paraoxonase/arylesterase: glutamine or arginine at position 191, for the respective A or B allozymes.

The paraoxonase/arylesterase gene is located close to the cystic fibrosis gene on chromosome 7. Human serum contains two paraoxonase/arylesterase allozymes, A and B, which differ in their substrate specificities and kinetic properties. Purified A, AB, and B esterases were digested with trypsin, and the resultant peptides were compared by high-performance liquid chromatography. The elution profiles were very similar for all three samples, except for (1) one peptide (i.e., peptide A) seen only in the A and AB profiles and (2) another peptide (i.e., peptide B) seen only in the B and AB profiles. Sequencing revealed that peptide A had glutamine at amino acid position 191, whereas peptide B was generated by cleavage on the carboxy side of position 191, presumably because there was a basic (trypsin-specific) amino acid at that position. Working independently, our laboratory and one other laboratory have sequenced the coding region for paraoxonase from human liver cDNA libraries and have identified two polymorphic sites: Arg/Gln at position 191 and Leu/Met at position 54. Using PCR amplification and direct sequencing of nucleotides in both polymorphic regions with genomic DNA, we have estimated the allelic frequencies and have determined their concordance with the serum paraoxonase allozyme phenotypes in 27 unrelated adults and in 16 members of a three-generation pedigree. Among unrelated individuals, the Met/Leu polymorphism at position 54 did not correlate with the serum esterase phenotype. In contrast, the particular amino acid at position 191 correlated perfectly with serum phenotypes: A-type individuals had Gln at position 191, and B-type individuals had Arg at position 191; AB-type serum was found only with the heterozygous (Arg/Gln) combination. Pedigree analysis showed both polymorphisms to be inherited in the expected Mendelian manner and confirmed that only the 191 polymorphism showed concordance with the serum paraoxonase/arylesterase phenotypes.     

Vasoactive factors in decompensated cirrhosis. Effect of acute plasma expansion

Plasma volume expansion was performed in 16 cirrhotic patients with ascites, 8 with avid sodium retention (sodium retainers) and 8 with normal sodium balance (sodium excretors). No natriuretic response was observed in sodium retainers (daily UNa = 7.1 +/- 1.5 mEq before expansion and 20.8 +/- 7.8 after expansion; p = not significant). After expansion plasma renin activity and plasma aldosterone showed a fall in both groups, whereas urinary kallikrein excretion decreased significantly in sodium retainers (27.1 +/- 9.7 before expansion and 7.8 +/- 6.4 after expansion; p less than 0.05). Baseline PGE were higher than normal in sodium retainers (997.0 +/- 134.3; p less than 0.02 vs. controls) and increased after expansion. Plasma octopamine was always within normal range. These results suggest that: a) reduction of effective plasma volume is not the main factor involved in sodium retention; b) the renin-angiotensin-aldosterone system has only a permissive role; c) prostaglandin system is activated and could have a protective role in maintaining renal function in cirrhotic patients.     

Administration of semisynthetic human insulin by a spray injector

The use of Jet injection in insulin administration pointed out the question whether this route could affect insulin absorption and plasma insulin profiles. To compare plasma insulin profiles following an administration of an identical insulin dose by jet injection or by conventional subcutaneous route (syringe with needle) 8 healthy subjects (age 24-28 yrs., non obese) were given at 09.00 h of two different days 200 mU/kg/BW of human semisynthetic regular insulin (Novo Actarapid) alternatively subcutaneously by a syringe with needle or transcutaneously by jet injection (DG 77 - Sicim - Gorizia). Before insulin administration and then 15, 30, 60, 90, 120 and 180 minutes after, blood samples were drawn for plasma insulin and C-peptide determination. Higher plasma insulin levels after administration by jet were found at 15' and 30' minutes (62,58 +/- 6,31 v.s. 36,94 +/- 3,31 microunits/ml at 15' and 76,51 +/- 9,60 v.s. 51,65 +/- 9,95 at 30', p less than 0,01 and p less than 0,005, paired Student t test). No difference could be observed for the other times. C-peptide was found to fall to undetectable values, confirming the nearly total suppression of endogenous insulin production. It is concluded that total regular insulin absorption does not differ after transcutaneous jet injection or administration by syringe with needle, but in the first case it is faster. This last finding should be considered in planning insulin treatment schedules.     

Action of veratridine on acetylcholinesterase in cultures of rat muscle cells

Studies on cultures of embryonic rat muscle cells have suggested that the presence of collagen-tailed forms may be correlated with spontaneous contractile activity: these forms disappear in the presence of tetrodotoxin which blocks the sodium channels involved in the propagation of action potentials. The effect of veratridine, a drug which maintains the sodium channels in the open state, was studied. It is shown here that in young cultures veratridine provoked a dramatic increase in total acetylcholinesterase activity and changed the distribution of the molecular forms of the enzyme, increasing the proportion and absolute amount of the A12 form. In order to elucidate the mechanism of action of this drug, the effects of various ions, ionophores, or other agents that modify the ionic permeabilities of membranes were also investigated.