connection it is of interest to note that other proteins such as collagens and high molecular weight glutenins show a higher solubility in acetate buffer solutions compared with other buffer systems these proteins resemble silk proteins in that they are repetitive amphiphilic block copolymers with a pi above 7 0 this suggests a preferential interaction of acetate ions with the proteins under acidic conditions possibly dependent on the small size of this carboxylic ion the ph value for obtaining the optimum spinning conditions for some of the buffer solutions was investigated the optimum ph value for spinning spidroin from ammonium acetate buffer solution was ph 4 7 u00b1 0 1 that of ammonium formate approximately ph 4 8 whilst the optima for the other buffer solutions was about ph 6 3 the latter values are close to the estimated ph in the duct of the spider and the ph of phosphate buffer solution for maximum sensitivity to shear in dilute spidroin solutions it is also close to the pk for the natural buffering of spidroin dope freshly removed from the spider 39 s silk gland histidine groups in proteins protonate between ph 6 and 7 strongly suggesting that the observed pk optimal sensitivity to shear and sol gel transition see below for spidroin in phosphate buffer involve the protonation of histidine.