Clinical and cytogenetic studies are reported in two infants with a stable ring G chromosome. Identification of the abnormal chromosomes was performed by the G-banding and the Q-banding methods.

Aneuploidy↗

PubMed1977

Interactions of alpha-chymotrypsin with peptides containing tryptophan or its derivatives at the C-terminus.

The interaction between alpha-chymotrypsin [EC 3.4.21.1] and peptide substrate or peptide inhibitor was investigated to determine how the secondary interaction influences the rate of hydrolysis or the binding and whether or not its effect is variable with alteration of the P1 residue which interacts with the specificity determining site of the enzyme. Kinetic analysis was carried out at pH 6.5 and 7.8 for substrates of the type Ac-Glyn-X-OMe and for inhibitors of the type Ac-Glyn-X-OH where X denotes tryptophan or its derivatives. With substrates containing tryptophan or Nin-formyltryptophan, the second-order rate of hydrolysis increases with increase of chain length. With substrates containing 2-(2-nitro-4-carboxyphenylsulfenyl)-tryptophan, however, the rate of hydrolysis decreases with elongation of the chain, due to an increase in Km(app). The corresponding inhibitors behave differently from the other series of inhibitors at pH 6.5. The results indicate that the influence of the secondary interaction on reactivity or binding is related to the structural features of the P1 residue.

Binding Sites↗

PubMed1977

Studies on papain catalysis with substrates containing the trans-p-phenylazobenzoyl group as a probe for hydrophobic interaction.

The susceptible bonds of substrates of the type PABz-GLYn-Arg-R (R=OCH3, n=0,1,2; R=OH, n=1,2) to papain [EC 3.4.22.2] have been identified. PABz-Arg-OMe was found to be approximately 30 times more reactive than benzoylarginine ethyl ester, due to a Km(app) value 25 times smaller. The finding that PABz-Gly2-Arg-OMe was specifically hydrolyzed at the ester bond with a second-order rate constant comparable with that of PABz-Arg-OMe indicated that the S4 subsite of the enzyme is capable of accommodating a large hydrophobic group. Other substrates were cleaved at the peptide bond one residue removed from the PABz group, in accord with the well-known fact that the S2 subsite interacts preferentially with a hydrophobic P2 residue. A negative charge on the substrate at the P2' or P3' position greatly decrease the acylation rate and also the noncovalent binding affinity. The hydrolysis of PABz-Arg-OMe and PABz-Gly2-Arg-OMe was little affected by the acridine dye proflavine.

Acridines↗

PubMed1977