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A set of fluorophenoxyanilides, designed to be simplified analogues of previously reported ω-conotoxin GVIA mimetics, were prepared and tested for N-type calcium channel inhibition in a SH-SY5Y neuroblastoma FLIPR assay. N-type or Cav2.2 channel is a validated target for the treatment of refractory chronic pain. Despite being significantly less complex than the originally designed mimetics, up to a seven-fold improvement in activity was observed.

Commercial acid proteinase from Rhizopus chinensis has been further purified by isoelectric focussing. Two forms of the enzyme (I and II) with very similar properties have been obtained. Like other fungal acid proteinases they activate trypsinogen at pH 3.4 and are inhibited by diazoacetyl norleucine methyl ester. Because of the lability of the label it has not been possible to isolate the active site peptide from a peptic digest. N-terminal amino acid sequences were determined for Rhizopus enzyme I (NH2∙Ala∙Gly∙Val∙Gly∙Thr∙Val∙Pro∙Asx∙Thr), for Rhizopus enzyme II (NH2∙Ala∙Gly∙Val∙Gly∙Thr∙Val∙Pro), and for penicillopepsin (NH2∙Ala∙Ala∙Ser∙Gly∙Val∙Ala∙Thr∙Asn∙Thr∙Pro∙Thr). The similarity in enzymic properties and in the sequence suggests that the Rhizopus enzymes are homologous with penicillopepsin and hence also with mammalian pepsins and calf chymosin.

A simple and efficient method has been developed for the synthesis of two anthranilamide-based non-peptide mimetics of ω-conotoxin GVIA. These anthranilamide derivatives aim to mimic the K2, R17, and Y13 residues of the peptide. The synthetic route described enables the rapid synthesis of anthranilamide analogues with identical alkyl chain lengths. The target compounds show affinity to rat N-type voltage gated calcium channels (Cav2.2) with EC50 values of 42 and 75 μM.

The reactivity of the α-amino group of isoleucine-16 of α-chymotrypsin towards nitrous acid at pH 4.0 and 0° is strongly dependent on ionic strength. Third-order deamination rate constants at low ionic strength (μ = 0.1 M) are 500–1000 times higher than those at high ionic strength (μ = 5.0 and 6.0 M) and are independent of the nature of the ions and the chymotrypsin concentration. Extrapolation to zero ionic strength of a plot of the logarithms of the constants against ionic strength leads to a value which is the same as that for the exposed α-amino group of the model compounds isoleucylvaline and valylvaline, and of the N-terminal isoleucine of pepsin. The deamination rate constant of the dipeptide valylvaline varies only two- to three-fold between ionic strength of 0.1 M and 6 M. The results suggest that the concept of a "buried" N-terminal as shown by X-ray analysis (carried out at pH 4.2 and ionic strength 9–11 M) requires modification; at low ionic strength (0.1 M) the reactivity of the N-terminal is only little below that of an exposed amino group, a fact which suggests that the amino group is much more available than shown by the X-ray analysis. The results are interpreted in terms of an effect of the ionic strength on the equilibrium between two conformational states of the enzyme.

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