Oxygen and sulfur esters of "inverse substrates": different responses of amidinophenol and amidinothiophenol in the activation of the rate of tryptic hydrolysis of the inverse esters

Kinetic parameters for the trypsin-catalyzed hydrolysis of the oxygen and sulfur "inverse substrates," p-amidinophenyl and p-amidinothiophenyl acetates and trimethylacetates, have been compared. The results suggest that both series of compounds are hydrolyzed via an identical pathway. Appreciable differences, however, were observed in the efficiency of the acylation process in both series, possibly reflecting the spatial requirements of the enzyme's active site toward these substrates. As reported previously, acceleration in deacylation by a positively charged molecule is a characteristic feature of trypsin-catalyzed hydrolysis of "inverse substrates." In the present investigation, it was shown that p-amidinothiophenol is ineffective as an activator, whereas its oxygen counterpart behaves as a potent activator toward oxygen and sulfur substrates. It is assumed that some ionic interaction between the enzyme and the ligand molecule could prevent the rate enhancement.     

Photolabeled sites with a tetrodotoxin derivative in the domain III and IV of the electroplax sodium channel.

Forty three percent of the labeled sites, at least, in the electroplax sodium channel with a photoactivable tetrodotoxin derivative were identified by probing protease-digested labeled fragments with several sequence-directed antibodies. They are located in the loop between segments S5 and S6 of domain IV, as well as the region containing transmembrane segment S6 and adjacent extracellular and cytoplasmic sequences in domain III. No photolabeled fragments were detected in the corresponding region of domain I. These results suggest that C-11 of tetrodotoxin where the photoreactive moiety is attached orients to the region between S5 and S6 in domain III and IV. Probable orientation of the tetrodotoxin molecule in sodium channels is considered by taking together with the recent report of the site-directed mutagenesis.     

Extensive polymorphism of ABO blood group gene: three major lineages of the alleles for the common ABO phenotypes

Polymorphism of the ABO blood group gene was investigated in 262 healthy Japanese donors by a polymerase chain reactions-single-strand conformation polymorphism (PCR-SSCP) method, and 13 different alleles were identified. The number of alleles identified in each group was 4 for A¹ (provisionally called ABO*A101, *A102, *A103 and *A104 according to the guidelines for human gene nomenclature), 3 for B (ABO*B101, *B102 and *B103), and 6 for O (ABO*O101, *O102, *O103, *O201, *O202 and *O203). Nucleotide sequences of the amplified fragments with different SSCP patterns were determined by direct sequencing. Phylogenetic network analysis revealed that these alleles could be classified into three major lineages, *A/*O1, *B and *O2. In Japanese, *A102 and *13101 were the predominant alleles with frequencies of 83% and 97% in each group, respectively, whereas in group O, two common alleles, *O101 (43%) and *O201 (53%), were observed. These results may be useful for the establishment of ABO genotyping, and these newly described ABO alleles would be advantageous indicators for population studies.     

IgE-mediated 14C-serotonin release from rat mast cells modulated by morphine and endorphins

The formaldehyde method was used to examine the interaction of PGE₁ with morphine, β-endorphin and Met-enkephalin on rat mast cells by their effects on IgE-mediated ¹⁴C-serotonin release. PGE₁ (2×10^?8?2×10^?5 M) caused a dose-related inhibition of the mediator release 1 min after an antigen challenge, and morphine (3×10^?7?3×10^?5 M) reversed this PGE₁ effect dose-dependently and stereospecifically; naloxone (2×10^?4 M) antagonized this action of morphine. β-Endorphin (3×10^?7?10^?5 M) and Met-enkephalin (3×10^?6?10^?4 M) mimicked this morphine action dose-dependently and were antagonized by naloxone (2×10^?4 M). These results suggest that morphine and endorphins modulate immunological mediator release from rat mast cells through opioid receptors.     

Diazipine, a novel photoaffinity probe for dihydropyridine receptors of calcium channels.

A new 1,4-dihydropyridine photoaffinity ligand, [3H]diazipine, has been assessed by binding and photolabeling, and compared with a currently used [3H]azidopine. [3H]Diazipine reversibly binds to skeletal muscle Ca2+ channels with a similar affinity to [3H]azidopine, but [3H]diazipine labels the channel two times more efficiently and no release of the incorported amount is observed after dithiothreitol treatment.