proteins expressed by recombinant dna methods in prokaryotic systems such as e . coli , are usually expressed as insoluble aggregates called inclusion bodies which require denaturation and renaturation ( refolding ) in order to recover the correctly folded biologically active form . the term “ inclusion bodies ” refer to the insoluble aggregates of proteins expressed by recombinant dna methods in microbial expression systems . the term “ oxidized forms of gcsf ” as used herein refers to methionine oxidation ( s ) at 1 or more site ( s ) in the gcsf molecule the term “ refolding buffer ” as used herein refers to a buffer that is used in renaturation or refolding of the protein of interest . the present invention provides a method for refolding gcsf obtained from inclusion bodies , wherein oxidized form of gcsf is reduced to less than 2 %. in an embodiment , the invention provides a method of refolding gcsf obtained from inclusion bodies by solubilization at about ph 11 to 12 wherein there is no incubation after the solubilization step and wherein the oxidized form of gcsf is reduced to less than 2 %. in an embodiment , the invention provides a method of refolding gcsf obtained from inclusion bodies by a ) solubilization at about ph 11 to about ph 12 wherein there is no incubation after the solubilization step . b ) adding a refolding buffer at about ph 8 to about ph 9 . c ) addition of cystine / cysteine at about ph 9 and incubation for about 16 hrs . wherein the oxidized forms of gcsf are reduced to less than 2 %. in an embodiment , the invention provides a method of refolding gcsf obtained from inclusion bodies by solubilization at about ph 11 to 12 wherein there is no incubation after the solubilization step and prior to adding the refolding buffer wherein the oxidized form of gcsf is reduced to less than 2 %. the invention is more fully understood by reference to the following examples . these examples should not , however , be construed as limiting the scope of the invention . cells containing recombinant gcsf in the form of inclusion bodies are resuspended in phosphate buffered saline ( pbs buffer ) in the ratio of 5 ml pbs buffer per gram of cell pellet . the cell suspension in pbs buffer is stirred on a magnetic stirrer for 20 min to make a homogenous solution . the cell suspension is centrifuged at a relative centrifugal force ( rcf ) of 13000 for 30 min at a temperature of 4 ° c . after centrifugation , supernatant is discarded and the pellet is resuspended in lysis buffer ( 50 mm tris and 10 mm edta ) in the ratio of 10 ml lysis buffer per gram of pellet . the cell suspension in lysis buffer is stirred gently on a magnetic stirrer for 20 min . the cell suspension is passed through the homogenizer two times at a pressure of 900 - 1000 bar till a drop in od 600 equivalent to 70 % is achieved . the cell lysate is collected and centrifuged at 13000 rcf for 30 min at 4 ° c . the pellet obtained is of the inclusion bodies . inclusion bodies obtained from example 1 , are solubilized with 8 m urea and water for injection ( wfi ). the ph of this suspension is adjusted to 11 to 13 by adding small quantities of 1 n sodium hydroxide solution . without incubation , the solubilization mixture from example 2 is diluted 20 times by directly adding the refolding buffer ( 25 mm tris , 1 mm edta and 0 . 6 m arginine and 5 % sorbitol ). the ph is adjusted to 8 . 6 - 9 . 4 by glacial acetic acid at ph 9 . 0 . after a 10 minute interval , the refolding mixture from example 3 is subject to redox shuffling by addition of 0 . 2 mm cysteine , after a 10 minute interval 1 . 8 mm cystine is added which is again followed by a 10 minute interval after which 0 . 2 mm cysteine is added . this mixture is incubated at 2 - 8 ° c . for 16 hours to obtain refolded gcsf .
provided is a method of refolding of recombinant gcsf that minimizes the generation of oxidized forms of gcsf by optimizing the refolding of inclusion bodies containing recombinant gcsf .