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    • The role of free amino groups of peptides and proteins in the Folin-Lowry and biuret methods

      B R Srinivasa L K Ramachandran

      Volume 2 Issue 2 June 1980 pp 99-106

    • Fulltext

       

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      Permanent link:
      https://www.ias.ac.in/article/fulltext/jbsc/002/02/0099-0106

    • Keywords

       

      Polymyxin B; acylation of polypeptides; reductive methylation of proteins; Folin-Lowry and Biuret methods; copper chelate of polymyxin B; formyl polymyxins B-Cu(II) chelates; Gramicidin S

    • Abstract

       

      On an equal weight basis polymyxin B and EM 49 which do not contain tyrosine or tryptophan yielded the same colour intensity as proteins in the Folin-Lowry and biuret methods. But, in the absence of reagent C (alkaline copper reagent) polymyxin B and EM 49 yielded no colour in the Folin-Lowry method. Mono-, di- and tri-formyl polymyxins B formed identical amounts of coloured complexes as polymyxin B in the two methods. However, the tetra- and penta-formyl polymyxins B yielded only one-fifth and one-sixth, respectively, of the expected colour in the Folin-Lowry method. Similarly, 40% and 30%, respectively, of the anticipated amount of colour is formed in the biuret method. Formylated and methylated lysozyme and bovine serum albumins form only 70–75% of the expected colour in the Folin-Lowry method. Since formation of colour by reduction of Folin reagent, in the Folin-Lowry method, is at least partly due to complexes of copper, it was inferred that polymyxin B as well as its mono-, di- and tri-formyl derivatives on the one hand and the tetra- and penta-formyl derivatives on the other differ in their ability to complex Cu(II) The former group of compounds was indeed found to complex as many as three Cu(II) ions whereas the tetra- and penta-formyl polymyxins B complexed only one equivalent, under conditions of excess Cu(II). Under conditions of low Cu(II), polymyxin B and all its derivatives complexed only one Cu(II). In proteins, sites other than amino groups which complex Cu(II) probably play a major role in the reduction of the Folin reagent, since methylated lysozyme and bovine serum albumin yield 70–75% of the colour formed by the unmodified proteins in the Folin-Lowry reaction.

    • Author Affiliations

       

      B R Srinivasa1 L K Ramachandran1

      1. Department of Biochemistry, Osmania University, Hyderabad - 500 007

    • Dates

       
      Published
      June 1980
      Manuscript received
      22 February 1980
      Manuscript revised
      10 May 1980

  • Journal of Biosciences | News

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    • To trigger further research on plant mitochondria, the Journal of Biosciences is bringing out a special issue titled "Plant Mitochondria: Properties and Interactions with Other Organelles".


      Plant mitochondria are quite distinct and have unique features, such as a cyanide-insensitive alternate pathway. They also interact with chloroplasts to optimize photosynthetic carbon assimilation.


      Submissions are welcome until 30 July 2023. The contributions can be original articles, short communications, reviews, or mini-reviews on any topic related to plant mitochondria.


      Authors can submit their articles online at https://www.editorialmanager.com/jbsc/default2.aspx

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