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蠶絲蛋白.ilk Protein Peptide 

Introduction: 

Silk protein hydrolyzed to be the mid-product what is pass the semi-permeable membrane,called silk peptide.The silk peptide which is used as raw material of cosmetic,which molecular weight is no more than 2000,and this molecular weight dissolved is good and is able to keep the good characteristics of the silk fibroid from crystallizing. 

Silk peptide upper molecular weight becoming permeable is good,and endued hair with natural blare,and increase elasticity of hair,and make hair figuration easily.Silk peptide upper molecular weight,can be absorbed by the skin and can filter the interior of the hair and provide necessary nutrient of the hair and can repair the damaged hair. 

There are two standards of the silk peptide used in cosmetic:one is solid peptide,also called silk peptide powder,the other is liquid silk peptide.In the produce proceed of the silk peptide,we can get two kinds average molecular weight 500 and 1,500,by control the conditions of the hydrolyze. 

BACKGROUND:

Much work has been done in the last decade to attempt to understand the relationship between the molecular structure of silks and their mechanical and physical properties. An excellent review will shortly be available [4]. The fibroin that is the only polypeptide in the dragline silk of Nephila clavipes spiders has a molecular weight of about 320 kD, which, if fully extended could be nearly 0.5 µm long. The recent partial sequencing of this silk [9] has greatly added to our understanding of the structure of these molecules, and its cloning and expression [4,6-7] affords us the potential of obtaining large quantities of pure spider dragline fibroin for in vitro experimentation.

Raman Spectroscopy:

Among the best ways to study protein secondary structure in solution is Raman spec tros copy. The technique has been underutilized primarily because of the expense and resultant scarcity of high quality equipment. Changes in f and u angles, in hydrogen bonding, and electrostatics of the environment all affect the vibrations of the peptide bonds, giving rise to a sensitivity of the amide normal modes to the secondary structure of the protein . In addition, subtle changes in sidechain vibrations can also be correlated with alterations in conformation or solvent. Both Fourier transform infrared spectroscopy (FTIR) and Raman scattering (both conventional and NIR-FTIR Raman) have strengths and weaknesses in studying polypeptide structure , but technical advances have recently greatly enhanced the utility of Raman spectroscopy. Nonspecific luminescence, for decades the nemesis of the technique, can be greatly reduced by using a red or near infrared laser sources. The new two-dimensional CCD detectors have excellent response in the far red, dynamic range of up to 105, and, when cooled to lN2 temperatures, better quantum efficiency than cooled PMTs with almost no noise (1 count per pixel per hour!). Because each of the thousands of CCD pixels has such high sensitivity, spectra that may have taken 12 hours to collect a decade ago may now be collected in 30 seconds, and smaller samples can be used at lower laser powers. For visible and some NIR frequencies, dispersive CCD-based systems are superior to any other detector type, including interferometers.

Figure 2. A Raman spectrum obtained from a single 2 µm thick strand of spider dragline silk. The laser beam was vertical (parallel to the slits) and focussed to a beam waist of approximately 50 µm; the fiber was held at a 15° angle tilted toward the monochromator slit. Collection time 20 sec, 300 mW 5145Å laser power, 100 µm slit.

The mainly amino acids of the silk powder protein have special function to the body, so the silk protein, hydrolyzed to amino acid or silk peptide, or partly hydrolyzed, its exploited prospect as nutrition health food is very alluring:
　

1.    Silk powder food:
　　

It is decided on the rate of digestion and nutrition function the silk made to food. Based on the animal experiment, the rate of digestion of silk powder is percent 27.0, the solution's is percent 47.0, if it is degradated to amino acid, the rate can be to above percent 90.0. From this we know the edibility of the silk powder is its low molecular weight level.
　　

The mainly edibility of the silk powder lie in amino acids composition and oligopeptide type. If only considered the amino acids content, the silk powder is only percent 6.0, this is negligible and is little worthy being nutrition. But from the composition of the amino acids types and content, it has unmeasurable natural function worthy. For example, the glycin percent 45 of all silk powder protein and Ser percent 12 can low the cholesterin. If you have more silk powder food, you can prevent hypertinsion, process insulin secrete, low blood sugar and prevent diabetes. The other example the alaninepercent 30 can process the alcohol metabolize, provide liver function and protect the liver. The tyrosine percent 6 can prevent cretinisin.
　　

Usually the silk is hydrolyzed to amino acids or oligopeptide by acid, so it becomes easier to be absorbed. Basis the necessary of the produce, we can make the silk powder into candy, dessert, cookies, noodles, bean curd, confiture and so on or make into capsule, troche and little bagged powder.
　　

2. Constitute of silk amino acids The silk is made of 18 kinds of amino acids, the amino acids names, chemical structure and molecular weight as following table 1:

The silk is hydrolyzed by the acid or alkali or enzyme to be the complex amino acids with nutrition, healthy, medicine and physiological function. Different molecular weight degradation of the silk have different physiological function to the body, and the function of the basis unit----amino acids, has been deeply known, the people is paying more and more attention to the exploiting the silk protein physiological function. The silk protein constitute of amino acids, characteristic constant, and the function are conclude as follow.

Table 1 Amino acid's Structure, Molecular Weight and Crystal Conformation

Table 2 shows the compositive ingredient of fibroin and sericin's amino acid. Through Table 2, we know both fibroin and sericin in silk protein contain 18 kinds of amino acid including the necessary amino acid of human body. The most amino acids in fibrion are Glycine, Alanine, Serine, Tyrosine. Besides these several amino acids, there are Aspartic acid and Glutamic acid etc in sericin. And the proportion of content is different, therefore these decide the different character. So we can choose from them according with application design and craft demand to product pure amino acid and amino acid's admixture.

Table 2 The member and content with amino acid in Fibroin and Sericin（mol %）

Attention: The "*" is the essential amino acid:

2.     The character of silk amino acid Because of amino（-NH2）and the carboxyl（-COOH），the amino acid have two characters of electrolyte. So we can divide them into polarity amino acid and non-polarity amino acid. The number of the amino and the carboxyl of the amino acid os different, so there are acidic amino acid and basic amino acid. Due to the different.    

degree in formate faction ( ) ,the amino acid have different affinity with water. These characters can sum up in table 3, we can use these character separation and extraction to get the amino acid we need.

Table 3 The polarity of the amino acid

4The amino acids function to body The different molecular weight decompound products have different value in use. For example, the polypeptide that molecular weight low 6000, and the small peptide include some compound amino acids, they might be made into functionality food and beverage. The polypeptide that molecular weight 2000~4000 is the excellent material of the makeup. The bipeptide, tripeptide and amino acids may be absorbed directly. So presently the value in use of the silk protein is inestimable.

Figure 4. Solubility, heat stability, and acid solubility of plant-produced synthetic silk proteins from tobacco leaves.

Secondary Protein - Structure