Geometry of binding of the benzamidine- and arginine-based inhibitors Nα-(2-naphthyl-sulphonyl-glycyl)-dl-p-amidinophenylalanyl-piperidine (NAPAP) and (2R,4R)-4-methyl-1-[Nα-(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulphonyl)-l-arginyl]-2-piperidine carboxylic acid (MQPA) to human α-thrombin : X-ray crystallographic determination of the NAPAP-trypsin complex and modeling of NAPAP-thrombin and MQPA-thrombin