The peptide Asp-Ala-His-NH-Me was subjected to removal of its N-terminal residue by transamination and scission. Despite the high affinity of the peptide for Cu2+ ions, they catalysed its transamination smoothly. Two main transamination products were found, a complication previously observed with another peptide with an N-terminal aspartic residue, but their scission gave a single product, Ala-His-NH-Me. This was subjected to a further cycle of transamination and scission, and gave a single product after each step. For scission of transaminated peptides it proved unnecessary to remove them from transamination reagents provided that transamination was stopped with EDTA before adding the scission reagent.

An analogue of ADP was made in which the terminal phosphono-oxy group, -O-PO(OH)2, has been replaced by the arsonomethyl group, -CH2-AsO(OH)2. This compound cannot form a stable analogue of ATP because anhydrides of arsonic acids are rapidly hydrolysed, so that any enzyme that phosphorylates ADP and accepts this analogue as a substrate should release orthophosphate in its presence. The analogue proves to be a poor substrate for 3-phosphoglycerate kinase (V/Km is diminished by a factor of 10(2)-10(3)) and a very poor substrate for pyruvate kinase (V/Km is diminished by a factor of 10(5)-10(6)). No substrate action was detected with adenyl kinase and creatine kinase.

1. Although only one activation peptide of bovine cationic trypsinogen has been reported previously, the peptide fraction obtained from activation mixtures shows several bands on paper electrophoresis at pH 6.5. 2. The major band was the peptide previously described. The band second in intensity of staining with ninhydrin (10-20% of that of the main band, as judged by eye) had an electrophoretic mobility consistent with its being related to the main peptide. It appeared on activation both of bulk commercial samples of trypsinogen and, as the Appendix shows, of samples prepared from pancreases obtained at the local abattoir. 3. The second peptide proved to be Phe-Pro-Val-Asp-Asp-Asp-Asp-Lys, and we conclude that it is another activation peptide. We discuss briefly the genetic and phylogenetic implications of our findings.

The analogue of fructose 1,6-bisphosphate in which the phosphate group, -O-PO3H2, on C-6 is replaced by the phosphonomethyl group, -CH2-PO3H2, was made enzymically from the corresponding analogue of 3-phosphoglycerate. It was a substrate for aldolase, which was used to form it, but not for fructose 1,6-bisphosphatase. It was hydrolysed chemically to yield the corresponding analogue of fructose 6-phosphate [i.e. 6-deoxy-6-(phosphonomethyl)-D-fructose, or, more strictly, 6,7-dideoxy-7-phosphono-D-arabino-2-heptulose]. This proved to be a substrate for the sequential actions of glucose 6-phosphate isomerase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Thus seven out of the nine enzymes of the glycolytic and pentose phosphate pathways so far tested catalyse the reactions of the phosphonomethyl isosteres of their substrates.