GB711246A - Process of producing insulin crystals with increased metal content - Google Patents

Abstract

Insulin crystals with a metal content above 0.16, and preferably above 0.25, milliequivalents per gram of crystal, are prepared by contacting crystalline insulin with an aqueous medium in which insulin crystals are insoluble or difficultly soluble and which has such a content of at least one of the metals zinc, cobalt, nickel, cadmium, copper, manganese and iron and such a pH value that the crystalline insulin takes up metal from the medium, and then separating it. Insulin crystals may be suspended in an aqueous medium containing one or more of the above metals in the form of a salt such as chloride, sulphate, nitrate, acetate or citrate, a hydroxide, oxide, metal complex or metal per se and having, or being adjusted to, a pH 2 to 9 and preferably 5 to 8 and especially 6 to 7, provided substances suppressing the solubility of the crystals are not present. The metal content of the medium is above 5 x A x 10-3 milliequivalents per litre, "A" designating the number of international units of insulin per mil of suspension. The pH is maintained by buffers such as acetate, borate, citrate, diethyl barbiturate, phosphate and maleate buffers, or mixtures thereof. Nitrate and phosphate buffers are not suitable for zinc-insulin crystals; but a phosphate buffer may be used for nickel-insulin crystals. Alternatively, insulin may be crystallized in an aqueous medium and insulin crystals of increased metal content produced by (a) adding the desired metal or metals, (b) changing the pH of the medium or (c) combining (a) and (b). Specification 709,927 is referred to.