The intestinal hormone guanylin and bacterial heat-stable enterotoxins (STs) are members of a peptide family that activates intestinal membrane guanylate cyclase. Two different peptides that activate the human intestinal T84 cell guanylate cyclase have been purified from urine and intestinal mucosa of opossums (Didelphis virginiana). The highly acidic peptide, QEDCELCINVACTGC, was named uroguanylin because it was isolated from urine and shares 53% identity with guanylin. A second peptide, SHTCEICAFAA-CAGC, was purified from urine and intestinal mucosa. This alanine-rich peptide was 47% identical to uroguanylin and 73% identical to human guanylin, suggesting that it may be an opossum homologue of guanylin. Synthetic uroguanylin-(2-15) (i.e., EDCELCINVACTGC) was 10-fold more potent than synthetic rat guanylin, but both peptides were less potent than Escherchia coli ST in the T84 cell cGMP bioassay. Uroguanylin-(2-15) and guanylin inhibited 12'I-ST binding to T84 cell receptors in competitive radioligand binding assays. Transepi-

The subunit c protein of mitochondrial ATP synthase accumulates in lysosomal storage bodies of numerous tissues in human subjects with certain forms of ceroid-lipofuscinosis, a degenerative hereditary disease. Subunit c appears to constitute a major fraction of the total storage-body protein. Lysosomal accumulation of subunit c has also been reported in putative animal models (dogs, sheep and mice) for ceroid-lipofuscinosis. In humans with the juvenile form of the disease, hydrolysates of total storage-body protein have been found to contain significant amounts of epsilon-N-trimethyl-lysine (TML). TML is also abundant in storage-body protein hydrolysates from affected dogs and sheep. These findings suggested that one or both of the two lysine residues of subunit c might be methylated in the stored form of the protein. The normal subunit c protein from mitochondria does not appear to be methylated. In a putative canine model for human juvenile ceroid-lipofuscinosis, residue 43 of the storage-body subunit c was previously found to be TML. In the present study, subunit c was isolated from the storage bodies of humans with juvenile ceroid-lipofuscinosis, and from sheep and mice with apparently analogous diseases. In all three species, partial amino acid sequence analysis of the stored subunit c indicated that the protein contained TML at residue 43. These findings strongly suggest that specific methylation of lysine residue 43 of mitochondrial ATP synthase plays a central role in the lysosomal storage of this protein.

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CH3(CH = CH)5CH = NC4H9 (compound 1) is structurally related to the Schiff base of retinal, the prosthetic group in visual pigments. Dilute solutions of a weak acid (phenol) and 1 in a hydrocarbon solvent, when subjected to decreasing temperature, show striking changes in electronic absorption spectra. Initially only the spectrum of compound 1 is present, but as the temperature is lowered, the absorbance of 1 decreases, and the spectrum of the H-bonded form of 1 appears and increases. Continued temperature lowering then causes a decrease in absorption of the H-bonded form and an appearance and rise in absorption of the proton-transferred form of 1. Concentrations of the various species are measured as a function of temperature, and by standard procedures, the thermodynamic constants for both reaction steps are computed. Values of delta H0 are taken as relative energies among the three ground states, and the lambda max value of each species yields relative energies among excited states. By employing data from electronic absorption spectroscopy, nuclear magnetic resonance (NMR) and theoretical calculations for retinal Schiff base, charge partitioning between nitrogen and the polyene chain and charge distribution among the carbon atoms of the polyene chain are calculated.