Mrs/Miss Medali,

The answer to your question is: By means of mass spectrometry.

However, I would like to focus your attention on our own-authored (mine and my co-author's contribution according to the authorship of the references shown, below) more recently developed theory and model formulas for quantification of mass spectrometric variable 'intensity.' They appear the only method currently available worldwide, which provide exact analytical quantitative and 3D structural information about analytes in complex mixture in terms of chemometrics. This means that there are exact chemometric linear correlative parameter (/r/ = 1.) Our method and model equations are tested, so far, at analyte concentration up to pg.(mL)-1 showing correlation between theory and experiment within values /r/ = 0.99997 - 1. Please, consider more detail on our theory and model formulas looking at references [1,2]. Also, please, consider our presentation on a forthcoming Conference devoted to the 'Medicinal Chemistry' [3]. In particular, consider the reference section, therein.

[1] Stochastic Dynamic Mass Spectrometric Approach to Quantify Reserpine in Solution; Bojidarka Ivanova, Michael Spiteller Analytical Chemistry Letters, 10 (2020) 703-721; Received 13 Oct 2020, Accepted 16 Dec 2020, Published online: 28 Jan 2021 Download citation https://doi.org/10.1080/22297928.2020.1865834

[2] Steroids, 164 (2020) 108750 Stochastic dynamic mass spectrometric quantification of steroids in mixture — Part II; Bojidarka Ivanova, Michael Spiteller.

[3] Conference Paper Mass spectrometric and quantum chemical treatments of molecu...

The presentation is also available on the Conference's web-page [https://ecmc2021.sciforum.net/] (section: General.)

Since, the theory and the model equations are our innovative quantitative approach, as mentioned before, published more recently, if you have any questions regarding their application to determine analytes in tissues both reflecting in mind questions concerning the theorytical background behind our equations or purely applied aspects of employment of our method, then, please, do not hesitate to ask them, herein, or during the Conference (01.11 - 30.11.2021.) They shall be addressed, accordingly.

If you have an antibody that specifically recognizes the peptide without background binding to the heart tissue, you could do it by immunohistochemistry.

Hi Tania Medali . You could biotinylate the peptide or have it synthesized with a terminal biotin label and use avidin-based detection to localize it.

I found only Steingrimur Stefansson 's answer relevant to the question.

I had come across the following article some time back while working on exosomes, but was not able to do much work on the topic. Hope this helps and does not complicate matters

Article Cardiac-specific delivery by cardiac tissue-targeting peptid...

Dear Tania, I just came across your very interesting technical question. According to the potentially useful article cited below, the following methods could be employed: immunohistochemistry, transmission electron microscopy, cryoimmunoelectron microscopy, and a specific radioimmunoassay. Please have a look at this paper:

Localization of Salmon Cardiac Peptide (sCP) in the Heart of Salmon (Salmo salar L.)

Article Localization of Salmon Cardiac Peptide (sCP) in the Heart of...

Unfortunately this paper has not been posted by the authors as public full text on RG. Perhaps you can access it through your institution. There is also a good chance that you can request the full text directly form the authors via RG because three of them have an RG profile.

Good luck with your research and best wishes, Frank Edelmann

Hello Bojidarka B. Ivanova thank you very much for your reply. I will take a look on your papers.

Hello Adam B Shapiro thank you for your reply. Unfortunately there is no antibody specific to this peptide because we synthetize it ourselves and it is not well studied.

Hello Steingrimur Stefansson thank you very much for your reply. That's a great advice I will try it.

Hello Ashutosh Acharya I will take a look on the paper that you sent, thank you !

Hello Frank T. Edelmann thank you so much for your reply! I will take a look on the paper, it will help me a lot !