No abstract

No abstract

The fully active semisynthetic enzyme formed by the non-covalent interaction of residues l-l 18 of bovine pancreatic ribonuclease and a synthetic tetradecapeptide containing residues 111-124 of the enzyme has allowed a direct test of the role of aspartic acid-121 in the functioning of the molecule. Replacement of this residue by asparagine results in a derivative that is 4.5% active against cytidine 2' ,3'-cyclic phosphate at pH 7.0 under standard assay conditions. Further studies with the same substrate at pH 5.8 reveal that the reduced activity results entirely from a diminished catalytic efficiency and not from a decreased affinity for substrate. Bovine pancreatic ribonucleaseActive site

No abstract

The cytoplasmic hemoglobin III from the gill of the symbiont-harboring clam Lucina pectinata consists of 152 amino acid residues, has a calculated Mm of 18,068, including heme, and has N-acetyl-serine as the N-terminal residue. Based on the alignment of its sequence with other vertebrate and nonvertebrate globins, it retains the invariant residues Phe45 at position CD1 and His98 at the proximal position F8, as well as the highly conserved Trp16 and Pro39 at positions A12 and C2, respectively. The most likely candidate for the distal residue at position E7 is Gln66. Lucina hemoglobin III shares 95 identical residues with hemoglobin II (J. D. Hockenhull-Johnson et al., J. Prot. Chem. 10, 609-622, 1991), including Tyr at position B10, which has been shown to be capable of entering the distal heme cavity and placing its hydroxyl group within a 2.8 A of the water molecule occupying the distal ligand position, by modeling the hemoglobin II sequence using the crystal structure of sperm whale metmyoglobin. The amino acid sequences of the two Lucina globins are compared in detail with the known sequences of mollusc globins, including seven cytoplasmic and 11 intracellular globins. Relative to 75% homology between the two Lucina globins (counting identical and conserved residues), both sequences have percent homology scores ranging from 36-49% when compared to the two groups of mollusc globins. The highest homology appears to exist between the Lucina globins and the cytoplasmic hemoglobin of Busycon canaliculatum.