23Phe,Tyr, and Trp have aromatic(芳香族)R groups .Phe and Tyr both have benzene rings. Tryptophan has an indole ring all three participate in hydrophobic interactions The-oh group in Tyr is an important functional group in proteins.(phosphorylation, hydrogen bond, etc) They are jointly responsible for the light absorption of proteins at 280 nm, a property used as a measure of the concentration of proteins
2.3 Phe, Tyr, and Trp have aromatic (芳香族) R groups •Phe and Tyr both have benzene rings. •Tryptophan has an indole ring. •All three participate in hydrophobic interactions. •The -OH group in Tyr is an important functional group in proteins. (phosphorylation, hydrogen bond, etc) •They are jointly responsible for the light absorption of proteins at 280 nm, a property used as a measure of the concentration of proteins
Phe,F,苯丙氨酸;Tyr,Y,络氨酸;Trp,W,色氨酸 Aromatic R groups COO Coo COO H3N--C-H H3N--C-H H3N--C-H CH2 CH2 CH2 C=CH NH OH Phenylalanine Tyrosine yptophan
Phe, F, 苯丙氨酸; Tyr, Y, 络氨酸; Trp, W, 色氨酸
Intensity of Intensity of incident transmitted light light A=0.012 Lam Monochromator Detector Sample cuvette with c moles/liter of absorbing species Tryptophan Lambert.-Beer’slaw: A=Log I/I=acl E, extinction coefficient; Tyrosine C, concentration; 0240250260270280290300310 l, optical length Wavelength(nm)
Lambert-Beer’s law: A=Log Io /I = ecl e, extinction coefficient; c, concentration; l, optical length
2.4 Positively charged(basic)and negatively charged(acidic)r groups The most hydrophilic r groups are those either positively or negatively charged Asp and glu have carboxyl in their r groups. They have net negative charge at pH 7.0, thus usually named as aspartate and glutamate (conjugate base names, instead of aspartic acid and glutamic acid, un-ionized form) Arg, Lys, and his have positively charged r groups at ph 7.0 Their r groups contain guanidino(胍基), amino, imidazole(咪唑基) groups respectively The side chain of His can be positively or uncharged depending on the local environment near ph 7.0
2.4 Positively charged (basic) and negatively charged (acidic) R groups •The most hydrophilic R groups are those either positively or negatively charged. •Asp and Glu have carboxyl in their R groups. They have net negative charge at pH 7.0, thus usually named as aspartate and glutamate (conjugate base names, instead of aspartic acid and glutamic acid, un-ionized form). •Arg, Lys, and His have positively charged R groups at pH 7.0. •Their R groups contain guanidino(胍基), amino, imidazole(咪唑基) groups respectively. •The side chain of His can be positively or uncharged depending on the local environment near pH 7.0
Iy,K,赖氨酸;Arg,R,精氨酸;His,H,组氨酸 Positively charged R groups COO COO COO H43N—C—HH3N—C-H H2N—C-H CH2 CH2 CH2 CH 2 CH2 C-NH CH CH 2 CH2 C-N CH2 NH H NH3 C=NH2 NH2 ysIne Arginine Histidine
Lys, K, 赖氨酸; Arg, R, 精氨酸; His, H, 组氨酸